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Drainage Laws by State: Neighbor Runoff Rules and Stormwater Permits

When water runs off one lot onto another, who pays for the damage depends on the state. The rules come mostly from court decisions, not statutes, and they fall into four families: common enemy, modified common enemy, civil law (natural flow) and reasonable use. Here’s what courts apply in each state and D.C., with the leading case where there is one, plus the stormwater and erosion rules that apply when a job moves dirt.

Quick answer

It depends on your state’s rule and on what changed. In our data, 21 states use a reasonable use rule, 16 a civil law (natural flow) rule and 9 a modified common enemy rule. Kansas and South Dakota split the rule between towns and rural land, and in Arizona, Wyoming and D.C. we couldn’t confirm a settled rule. What usually matters is the change you made: many entries name collecting, piping, concentrating or diverting water onto a neighbor as a way to become liable. Moving dirt has its own rules: a construction stormwater permit is required at 1 acre of disturbance in every state, and for smaller sites that are part of a larger development. Six states and D.C. also require an erosion and sediment control plan statewide for smaller jobs, such as 5,000 sq ft in Pennsylvania. Find your state below.

21states use a reasonable use rule

16states use a civil law (natural flow) rule

6states plus D.C. require an erosion plan below 1 acre statewide

3states plus D.C. where EPA issues the construction stormwater permit statewide

The four rules courts use

Common enemy: each owner may fend off surface water as they see fit, even if it ends up next door. None of our 51 entries uses it without limits. Kansas courts start from it inside city limits, but it doesn’t license harming a neighbor.
Modified common enemy (9 states): you may protect your land from runoff, within limits that vary by state, such as using reasonable care, avoiding unnecessary harm, or not collecting water and dumping it on a neighbor.
Civil law, or natural flow (16 states): the lower lot has to accept water that naturally flows onto it, and the upper owner can’t change that flow to make it worse for the neighbor below. Some of these states soften it: Pennsylvania allows ordinary grading and building, and California and Illinois add a reasonableness test.
Reasonable use (21 states): courts weigh whether the change was reasonable, looking at how useful it is, how much it changes the flow and how much harm it does.

These are mostly court-made rules, and the details vary within each label. Courts don’t always name the rule they apply; in 12 entries, including Pennsylvania, the label is ours, based on the rule the courts describe. Kansas and South Dakota use one rule for towns and another for rural land, and in Arizona, Wyoming and D.C. we couldn’t confirm a settled rule.

What this means if you regrade, add downspouts or build a patio

A few patterns run through the state entries below. They’re patterns, not promises: in a real dispute, the facts and your state’s cases decide it.

Ordinary improvements usually get more leeway than diverting water. In many entries, the rule starts from what you can do: regrade, build, drain or protect your lot from water, within limits. Pennsylvania’s courts, for example, say ordinary grading and building on your own lot isn’t enough by itself to make you liable.
Collecting water and sending it next door is the classic problem. Many entries name it outright: piping, channeling, concentrating or diverting water onto a neighbor can make you liable. The details vary: Alabama lets an upper owner concentrate flow to improve the property, as long as it doesn’t cause the lower owner substantial damage.
Reasonableness is the test in many states. The 21 reasonable use states weigh how reasonable the change was against the harm it caused, and several other states ask whether you used reasonable care or acted in good faith.
Local rules can be stricter than state law. Every state entry notes that cities, towns or counties can have their own grading, drainage or stormwater rules, and many say those rules can be stricter or reach smaller projects than the state’s.
Deadlines can be short. In 2026 the Texas Supreme Court applied a two-year deadline to these claims, and the clock can start when the flooding first happens. Maine requires a nuisance claim within 3 years.

If water is already damaging a neighbor’s property, or theirs is damaging yours, talk to a lawyer licensed in your state.

When a job needs a stormwater or erosion permit

Two layers apply when a job moves dirt. The baseline is a federal NPDES construction stormwater permit for disturbing 1 acre or more; every state entry uses that threshold, and under the federal rule a smaller site needs one too if it’s part of a larger common plan of development or sale that will disturb 1 acre or more, such as a lot in a subdivision. EPA issues the permit statewide in Massachusetts, New Hampshire, New Mexico and D.C. Elsewhere a state agency does, except on tribal land and at some federal sites, where EPA does.

Below 1 acre, the state rules in our data fall into four groups:

Statewide erosion plan triggers (6 states and D.C.): Pennsylvania and Delaware at 5,000 sq ft; Maryland at 5,000 sq ft or 100 cubic yards; New Jersey over 5,000 sq ft; Virginia at 10,000 sq ft (2,500 in Chesapeake Bay Preservation Areas); Connecticut over half an acre, through town rules (a lone single-family home is exempt); and D.C. at more than 50 sq ft.
Only in certain areas: within 200 ft of state waters in Georgia, within 500 ft of a lake or stream in Michigan, in New York City’s East of Hudson watershed (5,000 sq ft), near coastal waters in South Carolina’s Coastal Zone counties, and near surface water on steep slopes in New Hampshire (2,500 sq ft).
Case by case: in Kansas, Minnesota, Nevada and Washington, the state agency can require coverage for smaller sites.
Controls at any size: Maine requires erosion controls on all earth-moving work, with no size threshold and no permit; Wisconsin requires erosion and sediment controls at one- and two-family home construction sites under its Uniform Dwelling Code, shown on the building permit plan; and Pennsylvania requires erosion and sediment control practices on all earth disturbance.

Then check your town or county, which may require its own grading, drainage or stormwater permit for a smaller job.

Builder’s note: We work in Pennsylvania, one of the 6 states with a statewide erosion plan trigger below 1 acre. Disturbing 5,000 sq ft or more of ground, or any amount where the work could drain to a High Quality or Exceptional Value stream, requires a written erosion and sediment control plan (25 Pa. Code 102.4(b)(2)). 1 acre or more needs an NPDES construction stormwater permit, and so does a smaller job that is part of a larger plan of development, such as a lot in a subdivision (102.5(a)). Erosion and sediment control practices are required for any earth disturbance, however small (102.4(b)(1)). That 5,000 sq ft line counts total earth disturbance, so it can catch larger patio, wall and regrading jobs, and your township or borough may have its own stormwater ordinance on top.

Find your state:Jumps to your state’s full entry, with the official sources.

Drainage laws in all 50 states

State	Drainage rule	State erosion or permit rule below 1 acre?	Case, permits, local rules
Alabama	Civil law (natural flow)	None found	Details
Alaska	Reasonable use	None found	Details
Arizona	Unsettled	None found	Details
Arkansas	Modified common enemy	None found	Details
California	Civil law (natural flow)	None found	Details
Colorado	Civil law (natural flow)	None found	Details
Connecticut	Reasonable use	Yes: over half an acre, through town rules (a lone single-family home is exempt)	Details
Delaware	Reasonable use	Yes: 5,000 sq ft	Details
District of Columbia	Unsettled	Yes: over 50 sq ft	Details
Florida	Reasonable use	None found	Details
Georgia	Civil law (natural flow)	Only within 200 ft of state waters	Details
Hawaii	Reasonable use	None found	Details
Idaho	Civil law (natural flow)	None found	Details
Illinois	Civil law (natural flow)	None found	Details
Indiana	Modified common enemy	None found	Details
Iowa	Civil law (natural flow)	None found	Details
Kansas	Split rule	Only if the state agency requires it	Details
Kentucky	Reasonable use	None found	Details
Louisiana	Civil law (natural flow)	None found	Details
Maine	Reasonable use	Erosion controls on all earth work; no size or permit	Details
Maryland	Civil law (natural flow)	Yes: 5,000 sq ft or 100 cu yd	Details
Massachusetts	Reasonable use	None found	Details
Michigan	Civil law (natural flow)	Only within 500 ft of a lake or stream	Details
Minnesota	Reasonable use	Only if the state agency requires it	Details
Mississippi	Reasonable use	None found	Details
Missouri	Reasonable use	None found	Details
Montana	Modified common enemy	None found	Details
Nebraska	Modified common enemy	None found	Details
Nevada	Reasonable use	Only if the state agency requires it	Details
New Hampshire	Reasonable use	Only near surface water on steep slopes (2,500 sq ft)	Details
New Jersey	Reasonable use	Yes: over 5,000 sq ft	Details
New Mexico	Civil law (natural flow)	None found	Details
New York	Modified common enemy	Only in the NYC East of Hudson watershed (5,000 sq ft)	Details
North Carolina	Reasonable use	No: plan at 1 acre (local programs may go lower)	Details
North Dakota	Reasonable use	None found	Details
Ohio	Reasonable use	None found	Details
Oklahoma	Modified common enemy	None found	Details
Oregon	Civil law (natural flow)	None found	Details
Pennsylvania	Civil law (natural flow)	Yes: 5,000 sq ft (any size near HQ/EV streams)	Details
Rhode Island	Reasonable use	None found	Details
South Carolina	Modified common enemy	Only near coastal waters in Coastal Zone counties	Details
South Dakota	Split rule	None found	Details
Tennessee	Civil law (natural flow)	None found	Details
Texas	Civil law (natural flow)	None found	Details
Utah	Reasonable use	None found	Details
Vermont	Civil law (natural flow)	None found	Details
Virginia	Modified common enemy	Yes: 10,000 sq ft (2,500 in Chesapeake Bay Preservation Areas)	Details
Washington	Modified common enemy	Only if the state agency requires it	Details
West Virginia	Reasonable use	None found	Details
Wisconsin	Reasonable use	Erosion controls at home construction sites	Details
Wyoming	Unsettled	None found	Details

The rule courts apply to surface water between neighbors, and whether the state sets an erosion plan or permit rule for jobs under the 1-acre federal permit. “Unsettled” means we couldn’t confirm a rule; “Split rule” means one rule for towns and another for rural land. The leading case, permit details and local rules for each state are below.

State-by-state details

AlabamaOfficial source

Rule: Civil law (natural flow)
The rule: Modified civil law: the upper owner may alter or concentrate the flow to improve the property but may not unduly burden the lower owner by causing substantial damage.
Leading case: Street v. Tackett. 494 So. 2d 13 (Ala. 1986)
What it means for your yard: You can regrade, add downspouts or build a patio to improve your property, but if the change sends enough water onto a neighbor to cause substantial damage, you can be liable.
Construction stormwater permit: Alabama Department of Environmental Management (ADEM): 1 acre or more of land disturbance (or less if part of a larger common plan of development or sale totaling 1 acre or more)
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: Regulated sites must follow a Construction Best Management Practices Plan (CBMPP) prepared and certified by a Qualified Credentialed Professional. ADEM's page sets no lower statewide threshold.
Local rules: Cities and counties often have their own grading, land-disturbance or stormwater ordinances that can apply to smaller residential projects.
Good to know: Alabama lets you improve your property even if it changes how water drains, as long as you don't cause substantial damage to the neighbor below. Construction stormwater permits start at 1 acre of disturbance.

Sources: law.justia.com · adem.alabama.gov · epa.gov

AlaskaOfficial source

Rule: Reasonable use
The rule: Reasonable use: a landowner may drain surface water but is liable when the interference with its flow is unreasonable.
Leading case: Weinberg v. Northern Alaska Development Corp.. 384 P.2d 450 (Alaska 1963)
What it means for your yard: You can regrade, add downspouts or build a patio, but if the way you change the drainage is unreasonable and it harms a neighbor, you can be liable.
Construction stormwater permit: Alaska Department of Environmental Conservation (DEC), Division of Water (APDES program): 1 acre or more of total land disturbance (or less if part of a larger common plan totaling 1 acre or more, or if designated by the Director)
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: Current APDES Construction General Permit took effect Feb. 1, 2026 and expires Jan. 31, 2031 (DEC page). EPA, not DEC, covers construction in Indian country and Denali National Park and Preserve (EPA 2022 CGP Appendix B).
Local rules: Boroughs and cities often have their own grading, drainage or stormwater ordinances that can apply to smaller residential projects.
Good to know: Alaska uses a reasonableness test: you can manage water on your land, but not in a way that unreasonably harms a neighbor. Construction stormwater permits start at 1 acre.

Sources: law.justia.com · dec.alaska.gov · origin-awswest-www.epa.gov

ArizonaCheck locally

Rule: The law here is unsettled. Talk to an Arizona attorney about a drainage dispute.
What we found: Unsettled: a 1957 Arizona Supreme Court majority held an upper owner may not artificially increase the burden of surface water on the lower estate, while the dissent said Arizona follows the common-law (common enemy) approach from City of Tucson v. Dunseath; later Court of Appeals decisions treat water in washes and flood channels separately.
Leading case: Vantex Land and Development Co. v. Schnepf. 82 Ariz. 54, 308 P.2d 254 (1957)
What it means for your yard: Arizona's rule for yard runoff between neighbors is not clearly settled; the safest course is not to artificially increase or concentrate water onto a neighbor, and to talk to an Arizona attorney about any dispute.
Construction stormwater permit: Arizona Department of Environmental Quality (ADEQ), Water Quality Division (AZPDES): 1 or more acres of disturbance, or less than 1 acre if part of a larger common plan that will disturb 1 acre or more, discharging to protected surface waters or an MS4 (AZPDES CGP AZG2025-001, effective Aug. 29, 2025)
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: A SWPPP must be completed before filing the NOI through myDEQ; fees depend on acres disturbed. EPA covers Indian country in Arizona.
Local rules: Arizona cities and counties commonly require grading and drainage permits for residential lots.
Good to know: Arizona courts have not clearly settled which drainage rule applies between neighbors, so get local legal advice on a dispute. State construction stormwater permits start at 1 acre, and cities and counties often require grading and drainage permits.

Sources: courtlistener.com · courtlistener.com · azdeq.gov

ArkansasSecondary source

Rule: Modified common enemy
The rule: Modified common enemy: a landowner may defend against surface runoff without liability, unless the injury to the neighbor could have been avoided with reasonable effort and expense.
Why Secondary source: This rests on Arkansas Court of Appeals decisions. In Bilo the court quoted the rule as background but decided the case on other grounds, and no recent Arkansas Supreme Court opinion confirming it was found.
Leading case: Bilo v. El Dorado Broadcasting Co.. Ark. Ct. App. No. CA 07-507 (Feb. 13, 2008); quoting Boyd v. Greene County, 7 Ark. App. 110, 644 S.W.2d 615 (1983)
What it means for your yard: You can generally protect your land from runoff, but if your regrading or drainage work damages a neighbor in a way you could have avoided with reasonable effort and cost, you can be liable; work that diverts a defined watercourse (a channel with a bed and banks) is judged by whether it was reasonable.
Construction stormwater permit: Arkansas Department of Environmental Quality (DEQ): 1 acre or more (or part of a larger common plan): small sites 1 to under 5 acres are covered automatically with no NOI; large sites 5 acres or more must file an NOI, SWPPP and fee (permit ARR150000)
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: Small sites (1 to under 5 acres) must post a Notice of Coverage and keep a completed SWPPP on site, but do not file an NOI. The reissued ARR150000 is effective Nov. 1, 2026 to Oct. 31, 2031 (DEQ fact sheet).
Local rules: Cities and counties often have their own grading, drainage or stormwater ordinances that can apply to smaller residential projects.
Good to know: Arkansas courts let landowners protect their property from runoff, but you can be liable if you cause damage you could reasonably have avoided. Construction stormwater coverage starts at 1 acre; sites of 5 acres or more file a notice with DEQ.

Sources: caselaw.findlaw.com · adeq.state.ar.us · epa.gov

CaliforniaOfficial source

Rule: Civil law (natural flow)
The rule: Modified civil law with a reasonableness test: neither the upper nor the lower owner may act unreasonably, and each must take reasonable care to avoid injuring the other through surface water; if both act reasonably, the upper owner who changed the natural drainage generally bears the loss.
Leading case: Keys v. Romley. 64 Cal. 2d 396 (1966); reaffirmed and extended in Locklin v. City of Lafayette, 7 Cal. 4th 327 (1994)
What it means for your yard: If you regrade, add downspouts or build a patio, a court will ask whether you acted reasonably and whether your neighbor did too. Unreasonable changes that send water onto a neighbor can make you liable, and if both of you acted reasonably, the owner who changed the natural drainage usually bears the loss.
Construction stormwater permit: State Water Resources Control Board and the nine Regional Water Quality Control Boards: 1 acre or more of disturbance (or less than 1 acre if part of a larger common plan totaling 1 acre or more): Construction Stormwater General Permit, Order WQ 2022-0057-DWQ
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: Lake Tahoe sites use a separate Lahontan Regional Board permit; tribal lands fall under EPA. Sites of 1 to 5 acres with low rainfall erosivity may qualify for a waiver.
Local rules: California cities and counties commonly require grading permits and erosion control plans for residential projects well under 1 acre; check the local building or public works department.
Good to know: California courts judge drainage disputes by asking whether each neighbor acted reasonably; if both did, the one who changed the natural drainage usually bears the loss. Many cities and counties require a grading permit for jobs far smaller than the state's 1-acre stormwater permit threshold.

Sources: law.justia.com · law.justia.com · waterboards.ca.gov

ColoradoOfficial source

Rule: Civil law (natural flow)
The rule: Modified civil law (the Colorado Supreme Court's name for it): an upper owner may alter natural drainage conditions, provided the water is not sent down in a manner or quantity that does more harm to the lower land than before.
Leading case: Hankins v. Borland (as applied in Bittersweet Farms, Inc. v. Zimbelman). Hankins v. Borland, 163 Colo. 575, 431 P.2d 1007 (1967); Bittersweet Farms, Inc. v. Zimbelman, Colo. App. No. 97CA0339 (July 23, 1998)
What it means for your yard: Water may keep draining downhill the way it naturally does, and you can change your drainage, but not in a way that sends water onto your neighbor in a more harmful manner or volume than before.
Construction stormwater permit: Colorado Department of Public Health and Environment (CDPHE), Water Quality Control Division: 1 acre or more of disturbance, or part of a common plan of development or sale (General Permit COR400000, effective April 1, 2024 to March 31, 2029)
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: Threshold read from the current COR400000 permit linked from CDPHE's permit page (Part I.A.3.a). Some cities (Arvada, Durango, Golden, Lakewood) handle small sites under 5 acres locally. EPA covers federal facilities and Indian country.
Local rules: Colorado cities and counties often require grading, erosion control or stormwater permits for smaller projects; check locally.
Good to know: In Colorado, natural drainage onto lower land is allowed, but you can't change it in a way that does more harm to your neighbor than before. State construction stormwater permits start at 1 acre.

Sources: static.case.law · caselaw.findlaw.com · cdphe.colorado.gov · oitco.hylandcloud.com · epa.gov

ConnecticutOfficial source

Rule: Reasonable use
The rule: Reasonable use: a landowner dealing with surface water may take only such steps as are reasonable in light of all the circumstances (Page Motor Co. v. Baker, 1980, which replaced the common enemy privilege to repel water). Separately, a landowner still may not increase the volume of surface water flowing to a neighbor, or discharge it in a different volume or course than its natural flow, to the neighbor's substantial damage (Ferri v. Pyramid Construction, 1982).
Leading case: Page Motor Co. v. Baker. 182 Conn. 484 (1980)
What it means for your yard: Regrading, downspouts and patios are judged by what is reasonable under all the circumstances, and you can also be liable if your work increases the runoff reaching a neighbor or sends it onto their land in a different course or volume than it naturally flowed, causing substantial damage.
Construction stormwater permit: Connecticut Department of Energy and Environmental Protection (DEEP): 1 acre or more of total disturbance. Sites of 1 to under 5 acres with local land-use approval need no DEEP application; sites of 5 acres or more, and state, federal or municipal projects over 1 acre, must apply to DEEP
State rules below 1 acre: Under CGS 22a-329, town regulations must require a soil erosion and sediment control plan with any development application when the disturbed area is more than one-half acre; a single-family dwelling that is not part of a subdivision is exempt from those regulations (statute text as reproduced by DEEP). Towns may set stricter rules.
More on permits: DEEP's 2020 construction general permit took effect Dec. 31, 2020 and was set to expire Dec. 30, 2025; DEEP proposed reissuance on June 26, 2025 and has posted December 2025 reissuance documents (fact sheet dated January 2026). The 1-acre threshold is unchanged. The half-acre plan rule was read in the statute appendix of DEEP's 2002 Connecticut Guidelines for Soil Erosion and Sediment Control; the legislature's own statute page blocked automated reading.
Local rules: Connecticut towns review erosion and sediment control through planning, zoning and wetlands commissions, and many have their own grading and stormwater rules for small projects.
Good to know: Connecticut judges drainage disputes by what is reasonable, and you can still be liable for increasing runoff or redirecting it onto a neighbor. State stormwater permits start at 1 acre, and towns must require an erosion control plan for most development disturbing more than half an acre.

Sources: static.case.law · jud.ct.gov · portal.ct.gov · portal.ct.gov · portal.ct.gov

DelawareOfficial source

Rule: Reasonable use
The rule: Reasonable use: Delaware courts weigh the facts of each case under a 'reasonable user' standard instead of the rigid natural-flow rule.
Leading case: Weldin Farms, Inc. v. Glassman. 414 A.2d 500 (Del. 1980)
What it means for your yard: Courts look at whether your drainage change was reasonable under the circumstances; an unreasonable regrade, downspout or patio that floods a neighbor can make you liable.
Construction stormwater permit: Delaware Department of Natural Resources and Environmental Control (DNREC), Sediment and Stormwater Program; plans reviewed by delegated approval agencies: 1 acre or more of land disturbance (or less if part of a larger common plan of development)
State rules below 1 acre: Approved Sediment and Stormwater Management Plan required before disturbing land unless exempt; disturbances under 5,000 sq ft are exempt (7 Del. Admin. Code 5101, sections 1.3.1 and 1.4.2), so the practical trigger is 5,000 sq ft or more. Individual residential lots may qualify for standard plans (section 3.7).
More on permits: The 2026 NPDES Construction General Permit took effect March 11, 2026 for five years (DNREC fact sheet), replacing the 2021 permit; sites must operate under an approved Sediment and Stormwater Management Plan, which serves as the SWPPP. EPA, not DNREC, covers construction at federal facilities in Delaware (EPA 2022 CGP Appendix B).
Local rules: Counties and towns, and the delegated agencies that review plans, may add their own grading or drainage requirements.
Good to know: Delaware judges drainage disputes by whether each side acted reasonably. Disturbing 5,000 sq ft or more of ground needs an approved sediment and stormwater plan.

Sources: law.justia.com · documents.dnrec.delaware.gov · archive.regulations.delaware.gov · firststeps.delaware.gov

District of ColumbiaCheck locally

Rule: We couldn’t confirm a settled rule here. Talk to a D.C. attorney about a drainage dispute.
What we found: Not confirmed: we found no D.C. Court of Appeals opinion stating a neighbor-to-neighbor surface water rule.
What it means for your yard: There is no clear published D.C. rule to point to here; a homeowner with a drainage dispute should talk to a D.C. attorney.
Construction stormwater permit: U.S. EPA (NPDES construction general permit); DC Department of Energy and Environment (DOEE) runs the District's erosion and sediment control and stormwater management programs: 1 acre or more (or less if part of a larger common plan): EPA's 2022 Construction General Permit (DCR100000)
State rules below 1 acre: Erosion and sediment control plan required for projects that disturb or move more than 50 sq ft of land (DOEE); minor ESC projects under 5,000 sq ft do not need stormwater management review
More on permits: DC is one of the few places where EPA, not a state agency, issues the construction stormwater permit. DOEE's 50 sq ft trigger applies through the building permit process.
Local rules: In DC, DOEE and the building permit process handle erosion control and stormwater review directly; there are no separate county ordinances.
Good to know: We could not confirm which drainage rule D.C. courts apply between neighbors, so talk to a local attorney about a dispute. In D.C., disturbing more than 50 sq ft of soil needs an erosion and sediment control plan.

Sources: doee.dc.gov · origin-awswest-www.epa.gov · epa.gov

FloridaOfficial source

Rule: Reasonable use
The rule: Reasonable use: when a landowner improves land and surface water damages a neighbor, the reasonableness of each party's conduct is weighed.
Leading case: Westland Skating Center, Inc. v. Gus Machado Buick, Inc.. 542 So. 2d 959 (Fla. 1989)
What it means for your yard: You can regrade or build, but if the change sends water onto a neighbor, a court will weigh whether your conduct (and theirs) was reasonable; unreasonable changes can make you liable.
Construction stormwater permit: Florida Department of Environmental Protection (DEP), NPDES Stormwater Program: 1 or more acres of disturbance, or less than 1 acre if part of a common plan of development or sale, discharging to surface waters or an MS4 (Construction Generic Permit, DEP Document 62-621.300(4)(a))
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: Florida also has a separate state Environmental Resource Permit (ERP) program for stormwater management systems; we didn't check its thresholds for this guide.
Local rules: Florida counties, cities and water management districts often have their own grading, fill and drainage permit rules for residential lots.
Good to know: Florida uses a reasonable-use test for drainage disputes between neighbors. State construction stormwater coverage starts at 1 acre, but local fill and drainage permits often apply to smaller jobs.

Sources: law.justia.com · floridadep.gov

GeorgiaOfficial source

Rule: Civil law (natural flow)
The rule: Civil law (natural flow): the lower lot must accept water that naturally flows from the higher lot, but the upper owner may not collect and concentrate water and discharge it in greater quantity or in a different manner than nature would. (Label assigned from the rule; the opinion does not name a doctrine.)
Leading case: Terry v. Catherall. Ga. Ct. App. No. A16A0353 (July 12, 2016); quoting Green v. Eastland Homes, 284 Ga. App. 643 (2007) and Sumitomo Corp. of America v. Deal, 256 Ga. App. 703 (2002)
What it means for your yard: Your neighbor below has to accept water that naturally runs off your lot, but if you regrade, pipe downspouts or add a patio that collects water and sends more of it, or sends it in a new way, onto their land, you can be liable.
Construction stormwater permit: Georgia Environmental Protection Division (EPD); certified counties and cities act as local issuing authorities for land-disturbance permits under the Erosion and Sedimentation Act (O.C.G.A. 12-7-1 et seq.): 1 acre or more of land disturbance for stand-alone projects (GAR100001, effective Aug. 1, 2023 to July 31, 2028); common developments are covered under GAR100003 and infrastructure under GAR100002
State rules below 1 acre: Georgia's Erosion and Sedimentation Act requires a land-disturbing activity permit from the local issuing authority (or notice to EPD) unless an exemption applies. Projects disturbing less than 1 acre are exempt unless they are within 200 feet of the bank of any state waters or part of a larger common plan of 1 acre or more; single-family homes disturbing less than 1 acre (not part of a larger plan) are exempt but must still meet the Act's minimum erosion-control requirements (O.C.G.A. 12-7-7, 12-7-17).
More on permits: The GAR permits also require a 25-foot buffer along the banks of all state waters (50 feet for trout streams) unless a variance is granted. The 200-foot rule makes many small jobs near creeks subject to a local land-disturbance permit.
Local rules: Georgia counties and cities that are certified issuing authorities issue land-disturbance permits and often have their own grading and stormwater ordinances.
Good to know: In Georgia the lower lot must take natural runoff, but you can't collect water and dump more of it, or in a new way, onto a neighbor. State construction stormwater permits start at 1 acre, and a local land-disturbance permit can be needed for smaller jobs within 200 feet of a creek or other state waters.

Sources: caselaw.findlaw.com · epd.georgia.gov · gaswcc.georgia.gov

HawaiiOfficial source

Rule: Reasonable use
The rule: Reasonable use: each landowner may interfere with the natural flow of surface water, but is liable when the interference is unreasonable under the facts.
Leading case: Rodrigues v. State. 472 P.2d 509 (Haw. 1970)
What it means for your yard: You can change how water drains on your lot, but if the change is unreasonable and damages a neighbor, you can be liable.
Construction stormwater permit: Hawaii Department of Health (DOH), Clean Water Branch: 1 acre or more of land disturbance (or less if part of a larger common plan of development that will reach 1 acre): NPDES general permit, HAR Chapter 11-55 Appendix C
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: No lower statewide erosion-control plan threshold was found on DOH pages.
Local rules: Hawaii's counties have their own grading, grubbing and stormwater ordinances that commonly reach small residential projects.
Good to know: Hawaii uses a reasonable-use test for drainage disputes between neighbors. State construction stormwater coverage starts at 1 acre; county grading permits often apply to smaller jobs.

Sources: law.justia.com · health.hawaii.gov · health.hawaii.gov

IdahoOfficial source

Rule: Civil law (natural flow)
The rule: Civil law: a natural servitude of drainage means the lower owner must accept surface water that naturally drains onto it; the upper owner may not release water in unnatural concentrations that increase harm to the lower owner.
Leading case: Olson v. Moulton. Idaho S. Ct. Docket No. 44498, Opinion No. 24 (Mar. 13, 2018); quoting Dayley v. City of Burley, 96 Idaho 101, 524 P.2d 1073 (1974) and Burgess v. Salmon River Canal Co., 119 Idaho 299, 805 P.2d 1223 (1991)
What it means for your yard: Your downhill neighbor has to accept natural runoff, but you can't regrade or pipe water so that it lands on them in unnatural concentrations that cause more harm.
Construction stormwater permit: Idaho Department of Environmental Quality (DEQ), IPDES program: 1 or more acres of disturbance that discharges stormwater, or smaller sites that are part of a larger common plan (IPDES CGP IDR100000)
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: DEQ issues the construction general permit; EPA covers Indian country in Idaho (EPA 2022 CGP Appendix B).
Local rules: Idaho cities and counties often have their own grading, drainage and erosion control ordinances.
Good to know: Idaho requires the lower property to accept natural runoff, but you can't concentrate water onto a neighbor in a way that does more harm. State construction stormwater permits start at 1 acre.

Sources: law.justia.com · deq.idaho.gov · origin-awswest-www.epa.gov

IllinoisOfficial source

Rule: Civil law (natural flow)
The rule: Modified civil law: the upper owner has an easement for natural drainage but is liable for increasing the flow beyond what nature would produce; reasonable development is allowed ('good husbandry'), and in urban and suburban settings courts apply a reasonableness balancing test.
Leading case: Templeton v. Huss (as applied in Shulte v. Flowers). Templeton v. Huss, 57 Ill. 2d 134 (1974); Shulte v. Flowers, Ill. App. Ct. 4th Dist. No. 4-12-0132 (Feb. 8, 2013)
What it means for your yard: Natural runoff onto a lower lot is allowed, and reasonable improvements are too, but if your regrading, downspouts or patio unreasonably increase the water reaching a neighbor, especially in a town or subdivision, you can be liable.
Construction stormwater permit: Illinois Environmental Protection Agency (Illinois EPA), Bureau of Water: 1 acre or more of disturbance: General NPDES Permit for Construction Site Activities (ILR10); under the federal rule, smaller sites that are part of a larger common plan of 1 acre or more are also covered
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: Illinois EPA's page states the 1-acre threshold and no lower statewide threshold.
Local rules: Illinois counties and municipalities often require stormwater or grading permits for smaller residential projects.
Good to know: Illinois allows natural runoff and reasonable improvements, but in towns and subdivisions courts ask whether an increase in runoff onto a neighbor was reasonable. State construction stormwater permits start at 1 acre.

Sources: caselaw.findlaw.com · epa.illinois.gov

IndianaOfficial source

Rule: Modified common enemy
The rule: Common enemy with an exception: landowners may block or redirect diffuse surface water as they choose, but may not collect or concentrate it and cast it in a body onto a neighbor.
Leading case: Argyelan v. Haviland (reaffirmed in Haddix v. Klink). Argyelan v. Haviland, 435 N.E.2d 973 (Ind. 1982); Haddix v. Klink, Ind. Ct. App. No. 22A-CT-145 (July 29, 2022)
What it means for your yard: You can generally regrade or build to keep water off your land even if more ends up next door, but you can't gather water (for example with pipes, ditches or a downspout aimed at the line) and dump it in a concentrated flow onto a neighbor.
Construction stormwater permit: Indiana Department of Environmental Management (IDEM): 1 acre or more of land disturbance (or smaller sites that are part of a larger common plan): Construction Stormwater General Permit (CSGP)
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: Builders on individual lots inside a permitted development file a Construction Stormwater Residential Development Registration (State Form 53049) instead of their own NOI.
Local rules: Indiana counties and cities, including county drainage boards, often have their own drainage, grading and stormwater rules.
Good to know: Indiana follows the common enemy rule: you can generally keep water off your land, but you can't collect it and dump it onto a neighbor in a concentrated flow. State construction stormwater permits start at 1 acre.

Sources: law.justia.com · caselaw.findlaw.com · in.gov

IowaOfficial source

Rule: Civil law (natural flow)
The rule: Natural flow rule: the lower (servient) owner must accept natural drainage, but can get relief if the upper owner substantially increases the volume or substantially changes the manner of drainage and actual damage results. (Label assigned from the rule.)
Leading case: O'Tool v. Hathaway (as applied in Thill v. Mangers). O'Tool v. Hathaway, 461 N.W.2d 161 (Iowa 1990); Moody v. Van Wechel, 402 N.W.2d 752 (Iowa 1987); Thill v. Mangers, Iowa Ct. App. No. 22-0197 (Dec. 21, 2022)
What it means for your yard: Water can keep running downhill the way it naturally does, but if your regrading, downspouts or patio substantially increase the water reaching your neighbor or change how it gets there, and it causes damage, you can be liable.
State statute: Iowa Code 657.2(4) treats diverting water from its natural course to the injury of others as a nuisance (cited in Thill v. Mangers).
Construction stormwater permit: Iowa Department of Natural Resources (DNR): 1 acre or more of land disturbance (or part of a larger common plan totaling 1 acre or more): NPDES General Permit No. 2
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: DNR's page lists no lower statewide threshold.
Local rules: Iowa cities and counties often have their own grading, erosion control and stormwater ordinances.
Good to know: Iowa follows the natural flow rule: you can't substantially increase or change the runoff onto a neighbor's land if it causes damage. State construction stormwater permits start at 1 acre.

Sources: iowacourts.gov · iowadnr.gov

KansasOfficial source

Rule: Split rule
The rule: Split rule: by statute (K.S.A. 24-105) the civil law rule applies to agricultural land and highways outside city limits; inside incorporated cities the common-law common enemy rule still applies, though it does not license a landowner to harm neighbors.
Leading case: Williamson v. City of Hays. Kan. S. Ct. No. 87,771 (Mar. 7, 2003); discussing Liston v. Scott and K.S.A. 24-105
What it means for your yard: Inside a city, Kansas courts start from the common enemy rule, so you can generally protect your lot from runoff but cannot use it as license to harm a neighbor; on farmland outside cities, damming or diverting natural drainage onto a neighbor is unlawful under state statute.
State statute: K.S.A. 24-105 makes it unlawful to build or maintain a dam or levee that obstructs or discharges surface water to a neighbor's damage, but applies only to agricultural land and highways wholly outside incorporated cities.
Construction stormwater permit: Kansas Department of Health and Environment (KDHE), Bureau of Water: 1 or more acres of cumulative disturbance, or part of a larger common plan that will disturb 1 or more acres: General Permit S-MCST-2208-1 (KSR100000), effective Aug. 1, 2022 to July 31, 2027
State rules below 1 acre: Sites under 1 acre need coverage if KDHE notifies the owner that the project has significant pollution potential
More on permits: A site-specific stormwater pollution prevention plan is required. EPA covers Indian country in Kansas.
Local rules: Kansas cities and counties often have their own grading, drainage and stormwater ordinances.
Good to know: Kansas uses two rules: a state statute protects natural drainage on farmland outside cities, while inside cities courts start from the common enemy rule, which still doesn't let you harm a neighbor. State construction stormwater permits start at 1 acre; check with the city about local grading rules.

Sources: law.justia.com · kdhe.ks.gov

KentuckyOfficial source

Rule: Reasonable use
The rule: Reasonable use: courts weigh the upper owner's use of the land against the severity of harm to the lower owner.
Leading case: Klutey v. Commonwealth, Department of Highways. 428 S.W.2d 766 (Ky. 1967), modified on denial of rehearing June 14, 1968
What it means for your yard: You can improve your land, but if your regrading, downspouts or patio send water onto a neighbor, a court will weigh how reasonable your change was against the harm it caused.
Construction stormwater permit: Kentucky Energy and Environment Cabinet, Division of Water (KPDES program): 1 acre or more of clearing, grading or excavation (or smaller sites that are part of a larger common plan): KYR10 general permit
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: Division of Water fact sheet (June 2024) states no lower statewide threshold.
Local rules: Kentucky cities and counties often require their own erosion control or grading permits for smaller projects.
Good to know: Kentucky weighs the reasonableness of a drainage change against the harm it causes a neighbor. State construction stormwater permits start at 1 acre.

Sources: law.justia.com · eec.ky.gov

LouisianaOfficial source

Rule: Civil law (natural flow)
The rule: Civil law by statute: the lower estate must receive surface water that flows naturally from above, unless an act of man created the flow; the upper owner may not do anything to make that servitude more burdensome.
Leading case: Louisiana Civil Code arts. 655-656 (quoted in CV Land, LLC v. Miller's Lake, LLC). La. Ct. App. 3d Cir. No. 23-69 (Nov. 2, 2023)
What it means for your yard: Your downhill neighbor has to accept water that naturally flows from your lot, but you can't regrade, pipe or build in a way that makes that drainage burden heavier for them, and they can't block the natural flow either.
State statute: Louisiana Civil Code art. 655 (natural drainage) and art. 656 (obligations of the owners) set the rule directly.
Construction stormwater permit: Louisiana Department of Environmental Quality (LDEQ), Water Permits Division: 1 acre or more: small sites of 1 to under 5 acres are covered under LAR200000 without an NOI (SWPPP, posted notice and completion report required); sites of 5 acres or more need coverage under LAR100000
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: No permit fee for small construction sites.
Local rules: Louisiana parishes and cities often have their own drainage, fill and grading ordinances, especially in flood-prone areas.
Good to know: Louisiana law requires lower property to accept natural runoff, but you can't make the drainage burden on your neighbor heavier. State construction stormwater coverage starts at 1 acre.

Sources: legis.la.gov · legis.la.gov · caselaw.findlaw.com · deq.louisiana.gov

MaineOfficial source

Rule: Reasonable use
The rule: Reasonable use by statute: unreasonable use of land that alters the flow of surface water and unreasonably injures another's land, or unreasonably interferes with its reasonable use, is a nuisance (17 M.R.S. 2808, enacted 2005). Before the statute, Maine's common-law rule let owners control surface water on their own land, with liability mainly for artificial collection and discharge. (Label assigned from the statute's reasonableness test.)
Leading case: Johnson v. Whitten (pre-statute common-law rule). 384 A.2d 698 (Me. 1978); current rule set by 17 M.R.S. 2808
What it means for your yard: If you regrade, add downspouts or build a patio in an unreasonable way that changes runoff and unreasonably harms a neighbor's land, Maine law treats it as a nuisance; a claim must be brought within 3 years.
State statute: 17 M.R.S. 2808 (Alteration of surface water flow) makes unreasonable alteration of surface water flow that unreasonably injures another's land a nuisance; actions must be commenced within 3 years after the cause of action accrues.
Construction stormwater permit: Maine Department of Environmental Protection (DEP), Bureau of Water Quality / Land Resources: 1 acre or more of disturbed area, or less if part of a common plan that will disturb 1 acre or more: 2024 Maine Construction General Permit (effective Jan. 14, 2025 to Jan. 13, 2030); the state Stormwater Management Law also applies to projects of 1 acre or more of disturbed area in organized areas (with exemptions)
State rules below 1 acre: Maine's Erosion and Sedimentation Control Law applies to anyone who conducts an activity involving filling, displacing or exposing earthen materials, with no size threshold stated by DEP and no permit required; erosion controls are required on all such work.
More on permits: Stormwater Permit by Rule applicants must separately comply with the MCGP. Towns whose ordinances DEP approves can administer the Stormwater Management Law locally.
Local rules: Maine towns often regulate grading and stormwater through shoreland zoning and site plan ordinances.
Good to know: Maine law treats unreasonable changes to surface water flow that harm a neighbor as a nuisance, with a 3-year deadline to sue. Erosion controls are required on any soil disturbance, and the state stormwater law applies at 1 acre.

Sources: legislature.maine.gov · law.justia.com · maine.gov · maine.gov · maine.gov · maine.gov

MarylandOfficial source

Rule: Civil law (natural flow)
The rule: Natural flow with reasonable precautions: landowners are entitled to have surface water flow naturally over lower land, but upper owners may not artificially increase or concentrate the flow and must use reasonable precautions against harm. (Label assigned from the rule.)
Leading case: Mayor and City Council of Baltimore v. Abel (restating Battisto v. Perkins). Supreme Court of Maryland No. 26, Sept. Term 2025 (July 29, 2026); citing Battisto v. Perkins, 210 Md. 542 (1956) and Whitman v. Forney, 181 Md. 652 (1943)
What it means for your yard: Water may keep flowing downhill naturally, but if you regrade, pipe downspouts or add a patio that artificially increases or concentrates runoff onto a neighbor without reasonable precautions, you can be liable.
Construction stormwater permit: Maryland Department of the Environment (MDE); erosion and sediment control plans are approved by local approval authorities: 1 acre or more of planned total earth disturbance (or less if part of a common plan that will ultimately disturb 1 acre or more): General Permit No. 20-CP for Stormwater Associated with Construction Activity (effective April 1, 2023)
State rules below 1 acre: Grading permit and approved erosion and sediment control plan required unless less than 5,000 sq ft and less than 100 cubic yards are disturbed (state law minimum; local jurisdictions may be stricter)
More on permits: Local jurisdictions may require sediment controls even below the state 5,000 sq ft / 100 cubic yard threshold.
Local rules: Maryland counties and municipalities issue grading permits and may set stricter erosion control and stormwater thresholds than the state.
Good to know: Maryland lets water flow naturally downhill but bars artificially increasing or concentrating it onto a neighbor. Disturbing 5,000 sq ft or 100 cubic yards of soil generally needs a grading permit and erosion control plan.

Sources: mdcourts.gov · mde.maryland.gov · mde.maryland.gov · mde.maryland.gov

MassachusettsOfficial source

Rule: Reasonable use
The rule: Reasonable use: liability for surface water depends on whether the landowner is making a reasonable use of the land; Massachusetts abandoned the common enemy rule.
Leading case: DeSanctis v. Lynn Water & Sewer Commission. 423 Mass. 112 (1996); following Tucker v. Badoian, 376 Mass. 907 (1978) and von Henneberg v. Generazio, 403 Mass. 519 (1988)
What it means for your yard: Regrading, downspouts and patios are judged by whether your use of the land was reasonable; an unreasonable change that sends water onto a neighbor can be a nuisance.
Construction stormwater permit: U.S. EPA (Construction General Permit); MassDEP handles state Wetlands Protection Act stormwater standards and WM15 applications for sites near Outstanding Resource Waters: 1 acre or more (or part of a larger common plan): EPA 2022 Construction General Permit (MAR100000)
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: Massachusetts is one of the few states where EPA issues construction stormwater permits. MassDEP's Wetlands and Waterways program oversees stormwater standards under the Wetlands Protection Act, guided by the Massachusetts Stormwater Handbook.
Local rules: Massachusetts towns often have their own stormwater bylaws and conservation commission rules that reach small residential projects.
Good to know: Massachusetts judges drainage disputes by whether each owner used the land reasonably. EPA issues construction stormwater permits in Massachusetts starting at 1 acre, and town bylaws often apply to smaller jobs.

Sources: law.justia.com · law.justia.com · mass.gov · origin-awswest-www.epa.gov

MichiganOfficial source

Rule: Civil law (natural flow)
The rule: Natural flow: the lower estate must receive surface water from the upper estate in its natural flow, but the upper owner has no right to increase the amount of water that would naturally flow onto the lower estate. (Label assigned from the rule.)
Leading case: Bennett v. County of Eaton (as applied in Kernen v. Homestead Development Co.). Bennett v. Eaton County, 340 Mich. 330 (1954); Kernen v. Homestead Development Co., Mich. Ct. App. No. 205879 (Nov. 17, 1998)
What it means for your yard: Your downhill neighbor has to accept natural runoff, but if your regrading, downspouts or patio increase the amount of water reaching them, you can be liable.
Construction stormwater permit: Michigan Department of Environment, Great Lakes, and Energy (EGLE); Part 91 SESC permits are issued by County and Municipal Enforcing Agencies: 1 acre or more with a point-source discharge to state waters: construction storm water Permit-by-Rule (requires a Part 91 SESC permit first); 1 to 5 acres automatic, 5 acres or more file a Notice of Coverage
State rules below 1 acre: Part 91 soil erosion and sedimentation control (SESC) permit generally required for earth changes of 1 acre or more, or any size within 500 feet of a lake or stream
More on permits: The 500-foot lake-or-stream trigger catches many small residential jobs near water.
Local rules: Michigan counties and municipal enforcing agencies administer SESC permits and may have stricter local ordinances.
Good to know: Michigan requires the lower lot to take natural runoff, but you can't increase the water flowing onto a neighbor. A soil erosion permit is needed for 1 acre or more, or for any earth change within 500 feet of a lake or stream.

Sources: caselaw.findlaw.com · michigan.gov · michigan.gov

MinnesotaOfficial source

Rule: Reasonable use
The rule: Reasonable use: a landowner is liable only when a harmful interference with the flow of surface water is unreasonable, weighing the extent of harm, its foreseeability and the landowner's purpose.
Leading case: Pell v. Nelson. 201 N.W.2d 136 (Minn. 1972); following Enderson v. Kelehan, 226 Minn. 163, 32 N.W.2d 286 (1948)
What it means for your yard: You can drain and improve your lot, but if your regrading, downspouts or patio unreasonably send water onto a neighbor, judged by how much harm it does, whether it was foreseeable and why you did it, you can be liable.
Construction stormwater permit: Minnesota Pollution Control Agency (MPCA): 1 acre or more of soil disturbance, or less than 1 acre if part of a common plan of development or sale covering more than 1 acre
State rules below 1 acre: Any amount of soil disturbance can require permit coverage if MPCA determines the activity poses a risk to water resources
More on permits: EPA covers Indian country in Minnesota (EPA 2022 CGP Appendix B).
Local rules: Minnesota cities, counties and watershed districts often have their own grading, erosion control and stormwater rules for small projects.
Good to know: Minnesota judges drainage disputes by whether the interference with water flow was reasonable. State construction stormwater permits start at 1 acre, and watershed districts often regulate smaller jobs.

Sources: law.justia.com · stormwater.pca.state.mn.us

MississippiOfficial source

Rule: Reasonable use
The rule: Reasonable use: an upper landowner may not unreasonably alter natural drainage patterns to the detriment of the lower neighbor; anyone who diverts water must use reasonable care to prevent unnecessary injury. (Label assigned from the 'unreasonably alter' test; the court does not name a doctrine.)
Leading case: Martin v. Flanagan, LLC. Miss. S. Ct. No. 2001-CA-00300-SCT (May 23, 2002); quoting Hall v. Wood, 443 So. 2d 834 (Miss. 1983)
What it means for your yard: You can use and develop your land reasonably, but if your regrading, downspouts or patio unreasonably change natural drainage and hurt the neighbor below, you can be liable.
Construction stormwater permit: Mississippi Department of Environmental Quality (MDEQ): 1 acre or more: Small Construction General Permit for 1 to less than 5 acres; Large Construction General Permit (LCNOI) for 5 acres or more
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: MDEQ's page lists forms for each permit but does not say whether small sites file an NOI. The Small Construction General Permit expired April 30, 2024 and has been administratively continued while MDEQ works on reissuance.
Local rules: Mississippi cities and counties may have their own grading, drainage and stormwater ordinances.
Good to know: Mississippi courts ask whether an upper landowner unreasonably changed natural drainage to the harm of the neighbor below. State construction stormwater coverage starts at 1 acre.

Sources: caselaw.findlaw.com · caselaw.findlaw.com · mdeq.ms.gov

MissouriOfficial source

Rule: Reasonable use
The rule: Reasonable use: Missouri abandoned the modified common enemy doctrine for surface water runoff and adopted a reasonable use rule.
Leading case: Heins Implement Co. v. Missouri Highway & Transportation Commission. 859 S.W.2d 681 (Mo. 1993)
What it means for your yard: Regrading, downspouts and patios are judged by whether your conduct was reasonable; an unreasonable change that sends runoff onto a neighbor can make you liable.
Construction stormwater permit: Missouri Department of Natural Resources (DNR), Water Protection Program: 1 or more acres of disturbance (or less if part of a larger common plan of development or sale that will disturb 1 or more acres): land disturbance stormwater permit (MO-RA general permit)
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: DNR's page states no lower statewide threshold.
Local rules: Missouri cities and counties often require their own land disturbance or grading permits for smaller projects.
Good to know: Missouri uses a reasonable-use test for runoff disputes between neighbors. State land disturbance permits start at 1 acre.

Sources: law.justia.com · dnr.mo.gov

MontanaOfficial source

Rule: Modified common enemy
The rule: Common enemy limited by reasonable care: a landowner need not accept upstream surface water and may divert it, but must use reasonable care, without malice or negligence, to avoid damaging adjoining property.
Leading case: Winkowitsch v. Glacier Electric Cooperative, Inc.. 2023 MT 228 (Nov. 28, 2023); citing Covey v. Brishka, 2019 MT 164, 396 Mont. 362, 445 P.3d 785 and O'Hare v. Johnson, 116 Mont. 410, 153 P.2d 888 (1944)
What it means for your yard: You can protect your land from runoff, but when you regrade or redirect water you must use reasonable care not to damage your neighbor's property; careless or unreasonable diversion can make you liable.
Construction stormwater permit: Montana Department of Environmental Quality (DEQ), Water Protection Bureau (MPDES): 1 acre or more of total land disturbance (or smaller if part of a larger common plan that will disturb 1 acre or more): MTR100000, effective Jan. 1, 2023 to Dec. 31, 2027
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: EPA covers Indian country in Montana (EPA 2022 CGP Appendix B).
Local rules: Montana cities and counties may have their own grading and stormwater ordinances.
Good to know: Montana lets landowners fend off surface water, but you must use reasonable care not to damage a neighbor's property. State construction stormwater permits start at 1 acre.

Sources: law.justia.com · deq.mt.gov · deq.mt.gov

NebraskaOfficial source

Rule: Modified common enemy
The rule: Modified common enemy (label assigned): diffused surface water may be dammed, diverted or otherwise repelled if necessary and without negligence; but once it concentrates in a natural depression, draw, swale or other drainway, it must be allowed to pass. The Nebraska Supreme Court itself calls this the 'common-law rule' and says it rejected the strict common enemy doctrine.
Leading case: Romshek v. Osantowski (quoting Nichol v. Yocum). Romshek v. Osantowski, 237 Neb. 426, 466 N.W.2d 482 (1991); Nichol v. Yocum, 173 Neb. 298, 113 N.W.2d 195 (1962); see also Tall Grass Hills, L.L.C. v. Overholt, Neb. Ct. App. No. A-23-114 (May 7, 2024) (memorandum opinion, not designated for permanent publication)
What it means for your yard: You can generally keep diffuse runoff off your land if it's necessary and done without negligence, but you can't block or reroute water that runs in a natural swale or draw, and careless drainage work can make you liable.
State statute: Neb. Rev. Stat. 31-202 defines a watercourse (a depression or draw at least two feet below the surrounding land with a continuous outlet), and 31-201 lets owners drain land in the general course of natural drainage into a natural watercourse or depression without liability when the drain is wholly on their land (both quoted in Romshek).
Construction stormwater permit: Nebraska Department of Water, Energy, and Environment (DWEE; formerly NDEE): 1 acre or more of land disturbance, or less than 1 acre if part of a common plan of development or sale: NER210000 Construction Storm Water General Permit
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: New projects file an NOI at least 7 days before construction (NER210000 fact sheet dated June 3, 2021). EPA covers Indian country in Nebraska.
Local rules: Nebraska cities and counties often require their own grading or stormwater permits for smaller projects.
Good to know: Nebraska lets landowners repel diffuse runoff when necessary and done carefully, but water in a natural draw or swale must be allowed to pass. State construction stormwater permits start at 1 acre.

Sources: static.case.law · nebraskajudicial.gov · dwee.nebraska.gov · dwee.nebraska.gov

NevadaOfficial source

Rule: Reasonable use
The rule: Reasonable use: a landowner acting in good faith may drain surface water onto a neighbor only if the drainage is reasonably necessary, reasonable care is taken, and the benefit to the drained land outweighs the harm to the flooded land.
Leading case: County of Clark v. Powers. 611 P.2d 1072 (Nev. 1980)
What it means for your yard: If your regrading, downspouts or patio send water onto a neighbor, it has to be reasonably necessary, done with reasonable care, and worth more to you than the harm it does to them; otherwise you can be liable.
Construction stormwater permit: Nevada Division of Environmental Protection (NDEP), Bureau of Water Pollution Control: 1 acre or more (or less if part of a larger common plan that will disturb 1 acre or more): NVR100000
State rules below 1 acre: Sites under 1 acre can also need coverage if NDEP's Stormwater Branch determines the project could affect a receiving water or its tributaries within a quarter mile
More on permits: EPA covers Indian country in Nevada (EPA 2022 CGP Appendix B).
Local rules: Nevada counties and cities often have their own grading, drainage and dust/erosion control requirements.
Good to know: Nevada allows draining water onto a neighbor only when it is reasonably necessary, done with care, and the benefit outweighs the harm. State construction stormwater permits start at 1 acre.

Sources: law.justia.com · ndep.nv.gov

New HampshireSecondary source

Rule: Reasonable use
The rule: Reasonable use (1870 decision): a landowner may make reasonable modifications to the flow of surface water in the reasonable use and improvement of the land, judged by the importance of the improvement, the extent of the interference, the harm to neighbors and whether it was foreseeable. No modern New Hampshire Supreme Court decision restating the rule was found.
Why Secondary source: The leading case is from 1870, and no modern New Hampshire Supreme Court decision restating the rule was found.
Leading case: Swett v. Cutts. 50 N.H. 439 (1870); following Bassett v. Salisbury Manufacturing Co., 43 N.H. 569 (1862) (percolating water)
What it means for your yard: New Hampshire's highest court adopted a reasonable-use approach to surface water in 1870: you may make reasonable changes to how water flows when you improve your land, but unreasonable changes that harm a neighbor can make you liable. The leading case is very old and no recent decision restating it was found, so talk to a New Hampshire attorney before relying on it in a dispute.
Construction stormwater permit: U.S. EPA (Construction General Permit); NH Department of Environmental Services (NHDES) runs the state Alteration of Terrain (AoT) program: 1 acre or more (or part of a larger common plan): EPA 2022 Construction General Permit (NHR100000, statewide)
State rules below 1 acre: State Alteration of Terrain (AoT) permit required when disturbance cumulatively exceeds 100,000 sq ft of contiguous area (50,000 sq ft if any part is within the protected shoreland), or for more than 2,500 sq ft within 50 feet of surface water on steep (25%+) slopes draining toward it (Env-Wq 1502.58, 1503.02); smaller projects have a general permit by rule (Env-Wq 1503.03). 2025 legislation (SB 110, ch. 231, effective Sept. 13, 2025) changed AoT fees and tiers and directed a permit by notification for projects under 150,000 sq ft, so confirm current thresholds with NHDES.
More on permits: New Hampshire is one of the few states where EPA, not a state agency, issues construction stormwater permits. The AoT thresholds above are from the NHDES rules as posted on the General Court site (rule text effective 2017); RSA 485-A:17 was amended in 2025 (ch. 96, 141 and 231) and rules implementing SB 110 were due by Jan. 1, 2026.
Local rules: New Hampshire towns often regulate grading, driveways and stormwater through site plan, subdivision and zoning rules, and shoreland and wetlands permits may also apply.
Good to know: New Hampshire's highest court adopted a reasonable-use rule for surface water in 1870 and no later decision changing it was found, but because the case law is old, talk to a New Hampshire attorney about a real dispute. EPA issues construction stormwater permits in New Hampshire at 1 acre, and a state Alteration of Terrain permit applies to large disturbances (generally over 100,000 sq ft, or 50,000 near protected shorelands).

Sources: static.case.law · gencourt.state.nh.us · gc.nh.gov · origin-awswest-www.epa.gov · epa.gov

New JerseyOfficial source

Rule: Reasonable use
The rule: Reasonable use: New Jersey declared its adherence to the reasonable use rule for surface water.
Leading case: Armstrong v. Francis Corp.. 20 N.J. 320, 120 A.2d 4 (1956)
What it means for your yard: Regrading, downspouts and patios are judged by whether the change was reasonable; an unreasonable change that sends water onto a neighbor can make you liable.
Construction stormwater permit: New Jersey Department of Environmental Protection (NJDEP), Division of Water Quality; local Soil Conservation Districts under the NJ Department of Agriculture certify soil erosion and sediment control plans: 1 acre or more of clearing, grading and excavation: NJDEP construction stormwater general permit (5G3), applied for with a certified soil erosion and sediment control plan
State rules below 1 acre: Soil erosion and sediment control plan certified by the local Soil Conservation District required for construction activities disturbing more than 5,000 sq ft (NJ Soil Erosion and Sediment Control Act program)
More on permits: The NJ Department of Agriculture page did not say whether any single-family home exemption applies; check with the county soil conservation district.
Local rules: New Jersey municipalities also have stormwater control ordinances and grading or lot-development rules that can apply to small projects.
Good to know: New Jersey uses a reasonable-use test for drainage disputes between neighbors. Disturbing more than 5,000 sq ft needs a soil erosion and sediment control plan certified by the county soil conservation district.

Sources: law.justia.com · nj.gov · nj.gov

New MexicoOfficial source

Rule: Civil law (natural flow)
The rule: Civil law: a landowner has no right to collect surface water in an artificial channel and discharge it onto a neighbor's land to the neighbor's injury.
Leading case: Budagher v. Amrep Corp. (as applied in Walker v. LG Everist, Inc.). Budagher v. Amrep Corp., 97 N.M. 116, 637 P.2d 547 (1981); Walker v. LG Everist, Inc., 102 N.M. 783, 701 P.2d 382 (Ct. App. 1985)
What it means for your yard: Water can drain naturally downhill, but you can't collect it with a ditch, pipe or regraded channel and dump it onto your neighbor's land in a way that damages it.
Construction stormwater permit: U.S. EPA Region 6 (Construction General Permit); New Mexico Environment Department (NMED) Surface Water Quality Bureau provides state certification and guidance: 1 acre or more (or smaller sites in a common plan that will disturb 1 acre or more): EPA 2022 Construction General Permit (NMR100000)
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: New Mexico is one of the few states where EPA, not a state agency, issues construction stormwater permits (except Indian country, which has separate EPA coverage).
Local rules: New Mexico cities and counties have their own grading, drainage and erosion control ordinances.
Good to know: New Mexico follows the civil law rule: you can't channel collected water onto a neighbor's land to their injury. EPA issues construction stormwater permits in New Mexico starting at 1 acre.

Sources: law.justia.com · env.nm.gov · origin-awswest-www.epa.gov

New YorkOfficial source

Rule: Modified common enemy
The rule: Modified common enemy (label assigned; New York courts call it the common-law rule): an owner who improves land in good faith to fit it to a rational use is not liable for resulting changes in the flow of surface water, unless the water is drained onto the neighbor by artificial means such as pipes or ditches, or the improvements were not made in good faith.
Leading case: Kossoff v. Rathgeb-Walsh, Inc. (as applied in Ubiles v. Ngardingabe). Kossoff v. Rathgeb-Walsh, Inc., 3 N.Y.2d 583 (1958); Ubiles v. Ngardingabe, N.Y. App. Div. 1st Dept., Nos. 13730, 13730A (May 4, 2021)
What it means for your yard: Regrading or building a patio in good faith to improve your property generally won't make you liable for extra runoff, but piping or channeling water onto a neighbor, or making changes in bad faith, can.
Construction stormwater permit: New York State Department of Environmental Conservation (NYSDEC): 1 acre or more (SPDES Construction General Permit GP-0-25-001, effective Jan. 29, 2025 to Jan. 28, 2030); lower thresholds in the NYC East of Hudson watershed (5,000 sq ft or more) and within New York City (20,000 sq ft or more, or 5,000 sq ft or more of new impervious area)
State rules below 1 acre: 5,000 sq ft or more of disturbance in the New York City East of Hudson watershed triggers CGP coverage (and its erosion control plan); no statewide lower threshold outside those areas found
More on permits: Some agricultural, silvicultural and routine maintenance activities are exempt.
Local rules: New York towns, villages and cities often have their own stormwater, grading and erosion control laws that apply to smaller projects.
Good to know: New York generally protects owners who improve their land in good faith, but not if they pipe or channel water onto a neighbor. State construction stormwater permits start at 1 acre, or 5,000 sq ft in the NYC East of Hudson watershed.

Sources: static.case.law · caselaw.findlaw.com · dec.ny.gov

North CarolinaOfficial source

Rule: Reasonable use
The rule: Reasonable use: each possessor may make reasonable use of land even if surface water flow is altered, but is liable when a harmful interference with the flow is unreasonable and causes substantial damage.
Leading case: Pendergrast v. Aiken. 293 N.C. 201, 236 S.E.2d 787 (1977)
What it means for your yard: You can regrade, add downspouts or build a patio as a reasonable use of your land, but if the change unreasonably sends water onto a neighbor and causes substantial damage, you can be liable.
Construction stormwater permit: North Carolina Department of Environmental Quality (NCDEQ), Division of Energy, Mineral and Land Resources; some counties and cities run delegated local erosion control programs: 1 acre or more: NPDES construction general permit NCG01, obtained by e-NOI after the erosion and sedimentation control plan is approved
State rules below 1 acre: Erosion and sedimentation control plan must be submitted at least 30 days before disturbing 1 acre or more (Sedimentation Pollution Control Act); local programs may set lower thresholds
More on permits: Plan approval comes first, then the NCG01 Certificate of Coverage.
Local rules: Several North Carolina counties and cities run their own erosion control programs with lower thresholds than the state's 1 acre; check locally.
Good to know: North Carolina judges drainage disputes by whether the change in water flow was unreasonable and caused substantial damage. An erosion control plan is required for disturbing 1 acre or more, and some local programs set lower thresholds.

Sources: law.justia.com · deq.nc.gov

North DakotaOfficial source

Rule: Reasonable use
The rule: Reasonable use: a landowner acting in good faith may drain surface water onto another's land if there is a reasonable necessity for the drainage, reasonable care is taken to avoid unnecessary injury, and the benefit outweighs the harm; drainage done negligently or unreasonably can create liability.
Leading case: Young v. Hamilton. 332 N.W.2d 237 (N.D. 1983); following Jones v. Boeing Co., 153 N.W.2d 897 (N.D. 1967)
What it means for your yard: You can drain your land in good faith when it's reasonably necessary, but careless or unnecessary drainage that harms a neighbor can make you liable.
State statute: North Dakota also regulates drainage of ponds, sloughs and lakes by statute (the drain-permit statute discussed in Young, N.D.C.C. 61-01-22, was repealed in 1981; current drainage permit statutes were not checked).
Construction stormwater permit: North Dakota Department of Environmental Quality (DEQ): 1 or more acres of land disturbance (or smaller projects that are part of a larger development): NDPDES general permit NDR11
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: EPA covers Indian country in North Dakota (EPA 2022 CGP Appendix B).
Local rules: North Dakota cities, counties and water resource districts may have their own drainage and grading rules.
Good to know: North Dakota allows good-faith drainage that is reasonably necessary, done with reasonable care and worth more than the harm it causes. State construction stormwater permits start at 1 acre.

Sources: law.justia.com · deq.nd.gov

OhioOfficial source

Rule: Reasonable use
The rule: Reasonable use: a landowner is liable when a harmful interference with the flow of surface water is unreasonable; disputes are decided case by case under negligence principles.
Leading case: McGlashan v. Spade Rockledge Terrace Condo Development Corp. (as quoted in Novy v. Ferrara). McGlashan v. Spade Rockledge Terrace Condo Dev. Corp., 62 Ohio St.2d 55 (1980); Novy v. Ferrara, 2014-Ohio-1776 (11th Dist.)
What it means for your yard: If your regrading, downspouts or patio unreasonably interfere with how water flows and harm a neighbor, you can be liable; courts weigh the facts case by case.
Construction stormwater permit: Ohio Environmental Protection Agency (Ohio EPA), Division of Surface Water: 1 or more acres of ground disturbance, or part of a larger common plan that will ultimately disturb 1 or more acres: Ohio EPA construction stormwater general permit
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: Ohio EPA's page states no lower statewide threshold.
Local rules: Ohio counties and municipalities commonly have their own erosion, sediment and stormwater rules for smaller sites.
Good to know: Ohio judges runoff disputes by whether the interference with water flow was unreasonable. State construction stormwater permits start at 1 acre.

Sources: supremecourt.ohio.gov · epa.ohio.gov

OklahomaOfficial source

Rule: Modified common enemy
The rule: Common enemy modified by a rule of reason: a landowner may protect against surface water but may not sacrifice a neighbor's property to protect his own, and may not divert surface water from its usual course, collect it and convey it onto a neighbor's land to their injury.
Leading case: Moneypenney v. Dawson. 2006 OK 53, 141 P.3d 549; Iven v. Roder, 1967 OK 143, 431 P.2d 321
What it means for your yard: You can protect your property from runoff, but you can't collect water with ditches, pipes or regrading and send it onto your neighbor in a way that damages their land.
Construction stormwater permit: Oklahoma Department of Environmental Quality (DEQ), Water Quality Division: 1 acre or more (or under 1 acre if part of a larger common plan that will disturb 1 acre or more): OKR10, effective Oct. 18, 2022 to Oct. 17, 2027
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: EPA covers Indian country in Oklahoma and some discharges outside DEQ authority, such as oil and gas sites (EPA 2022 CGP Appendix B).
Local rules: Oklahoma cities often require their own grading, earth change or stormwater permits for smaller projects.
Good to know: Oklahoma lets landowners fend off surface water, but not by collecting it and sending it onto a neighbor's property. State construction stormwater permits start at 1 acre.

Sources: law.justia.com · law.justia.com · applications.deq.ok.gov

OregonOfficial source

Rule: Civil law (natural flow)
The rule: Civil law rule as modified in Oregon: an upper owner may drain surface water onto lower land in the quantities and places it would naturally drain, even through artificial drains that speed up the flow, with due regard for the lower owner; but may not divert water from its natural channels or concentrate it and discharge it where it otherwise would not have flowed.
Leading case: Garbarino v. Van Cleave (as applied in Gibson v. Morris). Garbarino v. Van Cleave, 214 Or 554, 330 P.2d 28 (1958); Rehfuss v. Weeks, 93 Or 25, 182 P 137 (1919); Gibson v. Morris, Or. Ct. App. No. A152724 (Apr. 29, 2015)
What it means for your yard: Water that naturally drains onto your downhill neighbor can keep doing so, even if your drains speed it up, but you can't divert it out of its natural path or collect it and send it onto their land at a new spot, and you must have due regard for their property.
Construction stormwater permit: Oregon Department of Environmental Quality (DEQ); some cities and agencies act as DEQ agents or cover small lots through local codes (1200-CN): 1 acre or more, including off-site support activities, or less than 1 acre if part of a common plan that will ultimately disturb 1 acre or more: NPDES 1200-C (effective Dec. 15, 2025 to Dec. 14, 2030)
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: In Local Qualified Program jurisdictions, an owner with a local construction permit is not required to apply to DEQ; those sites are covered under the 1200-CN permit through local codes.
Local rules: Oregon cities and counties often require erosion control permits for much smaller projects.
Good to know: Oregon lets natural drainage continue onto lower land, even if drains speed it up, but bars diverting or concentrating water onto a neighbor at a spot where it wouldn't naturally go. State construction stormwater permits start at 1 acre, and many cities regulate smaller jobs.

Sources: static.case.law · caselaw.findlaw.com · oregon.gov · oregon.gov

PennsylvaniaOfficial source

Rule: Civil law (natural flow)
The rule: Modified natural-flow rule: the upper owner is generally not liable for water that naturally flows downhill, and ordinary grading and building on one's own land does not by itself create liability for incidental effects; but the upper owner is liable for diverting surface water from its natural channel, gathering it by artificial means and discharging it in a body onto a neighbor, or unreasonably or unnecessarily increasing its quantity. (Label assigned from the rule; Pennsylvania courts do not name a doctrine.)
Leading case: Youst v. Keck's Food Service, Inc.. 94 A.3d 1057, 2014 PA Super 121 (Pa. Super. Ct. No. 1070 MDA 2013, decided June 11, 2014); applies Pa. Supreme Court precedent: Rau v. Wilden Acres, Inc., 376 Pa. 493 (1954); Chamberlin v. Ciaffoni, 96 A.2d 140 (Pa. 1953); Lucas v. Ford, 69 A.2d 114 (Pa. 1949); Pfeiffer v. Brown, 30 A. 844 (Pa. 1895); Shamnoski v. PG Energy, 858 A.2d 589 (Pa. 2004)
What it means for your yard: Pennsylvania generally doesn't hold you liable for rain that runs downhill the way it naturally would, and ordinary grading and building on your own lot isn't enough by itself. But if you divert runoff out of its natural path, collect it with pipes, downspouts or swales and send it onto a neighbor's land in a concentrated flow, or unreasonably increase how much reaches them, you can be liable for the damage.
Construction stormwater permit: Pennsylvania Department of Environmental Protection (DEP), Bureau of Clean Water: 1 acre or more of earth disturbance (or less if part of a larger common plan of development or sale that involves 1 acre or more): NPDES permit for Stormwater Discharges Associated with Construction Activities (PAG-01 or PAG-02 general permit, or an individual permit) under 25 Pa. Code 102.5(a)
State rules below 1 acre: Written erosion and sediment (E&S) control plan required for 5,000 sq ft or more of total earth disturbance, or any size with potential to discharge to High Quality or Exceptional Value waters (25 Pa. Code 102.4(b)(2)); E&S best management practices required for all earth disturbance regardless of size (102.4(b)(1))
More on permits: Chapter 102 applies to all earth disturbance; the 5,000 sq ft written-plan rule catches many residential patio, wall and regrading jobs that are far below the 1-acre permit threshold. A separate E&S permit is required for other earth disturbance of 5 acres or more that does not need an NPDES permit (102.5(d)). Upon complaint or inspection, DEP or the county conservation district can require the E&S plan to be submitted for review (102.4(b)(9)).
Local rules: Townships, boroughs and counties often have their own grading, stormwater management and driveway ordinances, which can require a permit or stormwater plan for much smaller projects.
Good to know: In Pennsylvania you're generally not liable for rain that naturally runs downhill, but you can be if you divert it, concentrate it onto a neighbor or unreasonably increase it. Disturbing 5,000 sq ft or more of ground requires a written erosion and sediment control plan, and a construction stormwater permit is needed at 1 acre.

Sources: caselaw.findlaw.com · law.justia.com · pacodeandbulletin.gov · pacodeandbulletin.gov · pa.gov · epa.gov

Rhode IslandOfficial source

Rule: Reasonable use
The rule: Reasonable use: a property owner's liability turns on the reasonableness of his actions, decided case by case as a question of fact.
Leading case: Butler v. Bruno. 341 A.2d 735 (R.I. 1975)
What it means for your yard: Regrading, downspouts and patios are judged by whether what you did was reasonable; an unreasonable change that floods a neighbor can make you liable.
Construction stormwater permit: Rhode Island Department of Environmental Management (RIDEM), Office of Water Resources (RIPDES program): 1 or more acres of disturbance, or less if part of a larger common plan exceeding 1 acre (RIPDES Construction General Permit)
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: RIDEM's page says the 2025 CGP runs until Sept. 26, 2026 and that RIDEM expects to reissue a new CGP on or before that date; the July 2026 draft (comments closed Aug. 17, 2026) keeps the 1-acre threshold and requires stormwater management plans at 5 acres or more, with RIDEM able to require them for 1 to under 5 acres. We couldn't confirm whether the 2026 permit is final; check RIDEM's page.
Local rules: Rhode Island cities and towns commonly require soil erosion and sediment control plans and stormwater review for smaller projects through local ordinances.
Good to know: Rhode Island judges drainage disputes by the reasonableness of each owner's actions. State construction stormwater permits start at 1 acre, and towns often regulate smaller jobs.

Sources: law.justia.com · dem.ri.gov · dem.ri.gov

South CarolinaOfficial source

Rule: Modified common enemy
The rule: Common enemy with a nuisance exception: a landowner may treat surface water as a common enemy, but may not use the land in a manner that creates a nuisance.
Leading case: Silvester v. Spring Valley Country Club. S.C. Ct. App. Op. No. 3297 (Feb. 12, 2001); citing Irwin v. Michelin Tire Corp., 288 S.C. 221, 341 S.E.2d 783 (1986)
What it means for your yard: You can generally protect your property from surface water, but if your drainage work creates a nuisance for a neighbor, for example by concentrating water onto their land, you can be liable.
Construction stormwater permit: South Carolina Department of Environmental Services (DES; formerly DHEC), Bureau of Water; local MS4 programs review first in some areas: 1 acre or more, or under 1 acre if part of a larger common plan totaling at least 1 acre (SCR100000, issued Feb. 27, 2026, effective Mar. 30, 2026 to Mar. 29, 2031)
State rules below 1 acre: In Coastal Zone counties, sites under 1 acre within one-half mile of a coastal receiving water also need coverage (2026 CGP section 1.3.1)
More on permits: Coastal projects may also need DES coastal zone (OCRM) review.
Local rules: South Carolina counties and cities with MS4 programs often have their own land disturbance and stormwater ordinances.
Good to know: South Carolina follows the common enemy rule, but you can't handle water in a way that creates a nuisance for a neighbor. State construction stormwater coverage starts at 1 acre, or smaller near the coast.

Sources: caselaw.findlaw.com · des.sc.gov · des.sc.gov

South DakotaOfficial source

Rule: Split rule
The rule: Split rule: civil law for rural land (the lower owner bears a drainage easement, but the upper owner may not discharge water by artificial means onto another's property); reasonable use for urban land.
Leading case: First Lady, LLC v. JMF Properties, LLC (urban); Zwart v. Penning (rural). First Lady, LLC v. JMF Properties, LLC, 2004 SD 69; Zwart v. Penning, S.D. No. 28306 (May 16, 2018)
What it means for your yard: In towns and cities, you can change drainage if the interference with water flow is reasonable; in rural areas, the downhill owner must accept natural drainage but you can't send water onto them by artificial means.
State statute: SDCL chapter 46A-10A (for example 46A-10A-20 and 46A-10A-70) governs rural drainage and drainage permits in natural courses.
Construction stormwater permit: South Dakota Department of Agriculture and Natural Resources (DANR): 1 or more acres of disturbance, or part of a larger common plan of development exceeding 1 acre (SDR100000)
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: EPA covers Indian country in South Dakota (EPA 2022 CGP Appendix B).
Local rules: South Dakota cities and counties may have their own drainage permits and grading rules.
Good to know: South Dakota uses a reasonableness test in towns and the civil law natural-drainage rule in the country. State construction stormwater permits start at 1 acre.

Sources: law.justia.com · caselaw.findlaw.com · danr.sd.gov

TennesseeSecondary source

Rule: Civil law (natural flow)
The rule: Natural drainage (label assigned; Tennessee appeals courts say the common enemy rule does not apply): lower land must receive water that naturally flows from higher land, a landowner may not gather or obstruct the natural flow so as to turn it onto a neighbor's property to the neighbor's injury, and wrongful interference with natural drainage is an actionable nuisance. These statements come from the Court of Appeals; no Tennessee Supreme Court decision was found.
Why Secondary source: The cases are from the Tennessee Court of Appeals; no Tennessee Supreme Court decision was found.
Leading case: Blackwell v. Butler (with Butts v. City of South Fulton). Blackwell v. Butler, 582 S.W.2d 760 (Tenn. Ct. App. 1978); Butts v. City of South Fulton, 565 S.W.2d 879 (Tenn. Ct. App. 1977); citing Slatten v. Mitchell, 22 Tenn. App. 547, 124 S.W.2d 310 (1938)
What it means for your yard: Tennessee appeals courts expect natural drainage to be left alone: your downhill neighbor has to take water that naturally runs off your lot, but if your regrading, downspouts or patio gather water or block its natural path and turn it onto a neighbor's property, causing damage, you can be liable for a nuisance. The cases are from the Court of Appeals, not the state Supreme Court.
Construction stormwater permit: Tennessee Department of Environment and Conservation (TDEC), Division of Water Resources: 1 acre or more of disturbance, or less if part of a larger common plan of development or sale (TNR100000; the final 2026 permit is effective Oct. 1, 2026 to Sept. 30, 2031)
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: Threshold and dates from TDEC's construction stormwater permit page, which says the final 2026 general permit has been issued; new forms were due on or around Oct. 1, 2026.
Local rules: Tennessee cities and counties with MS4 programs often require grading or land disturbance permits for smaller projects.
Good to know: Tennessee appeals courts say the 'common enemy' rule does not apply: downhill land must take natural runoff, but gathering or blocking water so it floods a neighbor can be a nuisance. There is no Tennessee Supreme Court decision on point, so get local legal advice on a dispute. State construction stormwater permits start at 1 acre.

Sources: static.case.law · law.justia.com · caselaw.findlaw.com · tn.gov

TexasOfficial source

Rule: Civil law (natural flow)
The rule: Statutory natural-flow rule: Texas Water Code 11.086 makes it actionable to divert or impound the natural flow of surface waters, or permit a diversion or impounding to continue, in a manner that damages another's property by overflow. (Label assigned from the statute; Texas common law was not researched.)
Leading case: Family Dollar Stores of Texas, LLC v. JLMH Investments, LLC. Tex. S. Ct. No. 24-0543 (June 26, 2026) (applying Tex. Water Code 11.086; claims held time-barred under the two-year limitations period); see also Michaelski v. Wright, Tex. App.-Houston [1st Dist.] No. 01-13-00490-CV (Aug. 7, 2014)
What it means for your yard: If your regrading, berm, wall or patio diverts or dams the natural flow of rainwater so it overflows onto your neighbor's property and damages it, you can be liable under state law. In 2026 the Texas Supreme Court applied a two-year deadline to these claims, and the clock can start when the flooding first happens.
State statute: Texas Water Code 11.086 governs diffuse surface water ('No person may divert or impound the natural flow of surface waters in this state'). Water in a defined channel, ditch or pipe, and floodwater, are treated differently (Michaelski).
Construction stormwater permit: Texas Commission on Environmental Quality (TCEQ): 1 acre or more (or part of a common plan): small sites of 1 to under 5 acres follow TXR150000 with an SWP3 and posted site notice (no NOI or fee); large sites of 5 acres or more file an NOI
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: Small-site operators must send the signed site notice to the receiving MS4 operator at least two days before starting. Under 1 acre and not part of a larger plan: no coverage required.
Local rules: Texas cities and counties often have their own grading, drainage and floodplain rules for residential projects.
Good to know: Texas law bars diverting or damming the natural flow of rainwater in a way that floods a neighbor. The deadline to sue is generally two years and can start running when the flooding first happens. State construction stormwater rules start at 1 acre.

Sources: txcourts.gov · caselaw.findlaw.com · tceq.texas.gov · tceq.texas.gov

UtahOfficial source

Rule: Reasonable use
The rule: Reasonable use: liability arises when a harmful interference with the flow of surface waters is unreasonable (Restatement of Torts section 833).
Leading case: Sanford v. University of Utah. 26 Utah 2d 285, 488 P.2d 741 (1971)
What it means for your yard: You can regrade, add downspouts or build a patio, but if the change unreasonably interferes with how water flows and harms a neighbor, you can be liable.
Construction stormwater permit: Utah Department of Environmental Quality (DEQ), Division of Water Quality (UPDES): 1 acre or more of soil disturbance, or less if part of a common plan of development or sale exceeding 1 acre (UPDES Construction General Permit UTRC00000, effective July 1, 2024; coverage renewed yearly)
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: EPA covers Indian country in Utah (EPA 2022 CGP Appendix B).
Local rules: Utah cities and counties commonly require their own land disturbance or grading permits for smaller projects.
Good to know: Utah uses a reasonable-use test for drainage disputes between neighbors. State construction stormwater permits start at 1 acre.

Sources: law.justia.com · deq.utah.gov

VermontOfficial source

Rule: Civil law (natural flow)
The rule: Natural flow: the lower owner must accept the natural flow of surface water, but an upper owner may not artificially increase it; concentrated discharge (for example through culverts) that damages lower land is actionable. (Label assigned from the rule; the opinion does not name a doctrine.)
Leading case: Powers v. Judd. 553 A.2d 139 (Vt. 1988)
What it means for your yard: Your downhill neighbor has to accept natural runoff, but if you collect water (with culverts, pipes or regrading) and discharge it onto them in a concentrated way that causes damage, you can be liable.
Construction stormwater permit: Vermont Agency of Natural Resources, Department of Environmental Conservation (DEC), Stormwater Program: 1 acre or more of total earth disturbance (or less if part of a larger common plan that will disturb 1 acre or more): Construction General Permit 3-9020, issued June 20, 2025
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: EPA covers only federal facility construction in Vermont (EPA 2022 CGP Appendix B).
Local rules: Vermont towns may regulate grading and stormwater through zoning and subdivision bylaws.
Good to know: Vermont requires lower land to accept natural runoff, but you can't artificially increase or concentrate water onto a neighbor. State construction stormwater permits start at 1 acre.

Sources: law.justia.com · dec.vermont.gov

VirginiaOfficial source

Rule: Modified common enemy
The rule: Modified common enemy: surface water is a common enemy each landowner may fight off as best he can, provided he does so reasonably and in good faith and not wantonly, unnecessarily or carelessly; no one may injure another by interfering with water in a natural channel or watercourse.
Leading case: Collett v. Cordovana. Va. S. Ct. Record No. 141297 (June 4, 2015); quoting Mullins v. Greer, 226 Va. 587, 311 S.E.2d 110 (1984) and McCauley v. Phillips, 216 Va. 450, 219 S.E.2d 854 (1975)
What it means for your yard: You can regrade or build to keep water off your property, but you must act reasonably and in good faith, not carelessly or unnecessarily, and you can't interfere with water in a natural channel to a neighbor's harm.
Construction stormwater permit: Virginia Department of Environmental Quality (DEQ); localities run most Virginia Erosion and Stormwater Management Programs (VESMPs) and erosion control programs: 1 acre or more (or less if part of a larger common plan that will disturb 1 acre or more): Virginia construction general permit (2024 general VPDES permit, July 1, 2024 to June 30, 2029)
State rules below 1 acre: Erosion control and water quantity criteria apply to land disturbance of 10,000 sq ft or more, or 2,500 sq ft or more in Chesapeake Bay Preservation Areas (other than single-family detached homes, which localities may also regulate); localities may set lower thresholds (Va. Code 62.1-44.15:34(E))
More on permits: Localities under the Chesapeake Bay Preservation Act may regulate single-family homes at 2,500 sq ft. Minor activities such as home gardens are exempt regardless of size (62.1-44.15:34(F)).
Local rules: Virginia counties, cities and towns administer land-disturbance permits and often set thresholds below the state's 10,000 sq ft.
Good to know: Virginia lets landowners fend off surface water if they act reasonably and in good faith, but not by interfering with water in a natural channel to a neighbor's harm. Disturbing 10,000 sq ft or more (2,500 sq ft in Chesapeake Bay Preservation Areas) triggers erosion control requirements, and many localities set lower limits.

Sources: caselaw.findlaw.com · law.justia.com · deq.virginia.gov · law.lis.virginia.gov

WashingtonOfficial source

Rule: Modified common enemy
The rule: Common enemy with three limits: landowners may not block a watercourse or natural drainway, may not collect water and discharge it onto a neighbor in greater quantities or a different manner than its natural flow, and must use due care when altering surface water flow.
Leading case: Currens v. Sleek. Wash. S. Ct. No. 66830-2 (en banc, Sept. 9, 1999)
What it means for your yard: You can generally change drainage on your lot, but you can't block a natural drainway, pipe or channel water onto a neighbor in a greater amount or different way than it naturally flowed, or make changes carelessly.
Construction stormwater permit: Washington State Department of Ecology: 1 acre or more, or smaller sites that are part of a larger common plan that will disturb 1 acre or more, discharging stormwater to surface waters (Construction Stormwater General Permit, effective Jan. 1, 2026 to Dec. 31, 2030)
State rules below 1 acre: Sites of any size can need coverage if Ecology determines they are a significant pollutant source or could violate water quality standards
More on permits: EPA covers Indian country and construction by federal operators in Washington (EPA 2022 CGP Appendix B).
Local rules: Washington cities and counties commonly require clearing, grading and drainage review for small residential projects.
Good to know: Washington follows a modified common enemy rule: you can't block natural drainways, dump collected water on a neighbor, or alter drainage carelessly. State construction stormwater permits start at 1 acre.

Sources: caselaw.findlaw.com · ecology.wa.gov

West VirginiaOfficial source

Rule: Reasonable use
The rule: Reasonable use: in dealing with surface water a landowner may take only such steps as are reasonable, weighing the actor's advantage against the neighbor's disadvantage and social utility; reasonableness is usually a jury question.
Leading case: Whorton v. Malone. W. Va. S. Ct. App. No. 28724 (June 15, 2001); following Morris Associates, Inc. v. Priddy, 181 W. Va. 588, 383 S.E.2d 770 (1989)
What it means for your yard: Regrading, downspouts and patios are judged by whether your steps were reasonable, weighing your benefit against your neighbor's harm; good intentions alone don't make a harmful diversion reasonable.
Construction stormwater permit: West Virginia Department of Environmental Protection (WVDEP), Division of Water and Waste Management: 1 acre or more of earth disturbance: construction stormwater general permit WV0115924 (effective April 6, 2024 to April 5, 2029)
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: WVDEP's program page states no lower threshold.
Local rules: West Virginia cities and counties may have their own grading, floodplain or stormwater ordinances.
Good to know: West Virginia judges drainage disputes by whether a landowner's steps were reasonable. State construction stormwater permits start at 1 acre.

Sources: caselaw.findlaw.com · dep.wv.gov

WisconsinOfficial source

Rule: Reasonable use
The rule: Reasonable use: Wisconsin rejected the common enemy doctrine and adopted the Restatement of Torts reasonable use rule; liability depends on whether the invasion is unreasonable.
Leading case: State v. Deetz. 66 Wis. 2d 1, 224 N.W.2d 407 (1974)
What it means for your yard: If your regrading, downspouts or patio unreasonably send water onto a neighbor, you can be liable; courts weigh the reasonableness of the change.
Construction stormwater permit: Wisconsin Department of Natural Resources (DNR): 1 or more acres of land disturbance (WPDES Construction Site Storm Water Discharge Permit)
State rules below 1 acre: Erosion and sediment control practices are required at one- and two-family dwelling construction sites under the state Uniform Dwelling Code (SPS 321.125), with erosion control measures shown on the plan submitted with the UDC permit application (SPS 320.09); the Department of Safety and Professional Services administers these rules for sites under 1 acre, and DNR has sole jurisdiction at 1 acre or more (DSPS history of Wisconsin's soil erosion program, rev. 3/2016).
More on permits: The one- and two-family dwelling erosion control rules above come from DSPS's own history of the program (rev. 3/2016), because the rule text itself wouldn't load for us; check current requirements with DSPS.
Local rules: Wisconsin counties and municipalities commonly have construction site erosion control and stormwater ordinances that apply to smaller projects.
Good to know: Wisconsin uses a reasonable-use test for drainage disputes between neighbors. State construction site stormwater permits start at 1 acre.

Sources: law.justia.com · dnr.wisconsin.gov · dsps.wi.gov

WyomingCheck locally

Rule: We couldn’t confirm a settled rule here. Talk to a Wyoming attorney about a drainage dispute.
What we found: Not confirmed: the Wyoming Supreme Court opinion checked treats water reaching a neighbor's land as a negligence question (reasonable care in directing irrigation or waste water) without naming a surface-water doctrine.
Leading case: Reed v. Cloninger. Wyo. S. Ct. No. 05-74 (Mar. 24, 2006); citing Howell v. Big Horn Basin Colonization Co., 14 Wyo. 14, 81 P. 785 (1905)
What it means for your yard: Wyoming courts have treated damage from water directed onto a neighbor's land as a matter of reasonable care, but no clear rule for ordinary yard runoff was confirmed; talk to a Wyoming attorney about a dispute.
Construction stormwater permit: Wyoming Department of Environmental Quality (DEQ), Water Quality Division (WYPDES): 1 acre or more: Small Construction General Permit for 1 to under 5 acres (no application or NOI; follow permit provisions); Large Construction General Permit for 5 acres or more (NOI, SWPPP, fee and map)
State rules below 1 acre: No statewide rule below the 1-acre permit found; check your county and town.
More on permits: A rainfall erosivity waiver may be available for small sites with an R factor under 5. EPA covers Indian country in Wyoming.
Local rules: Wyoming cities and counties may have their own grading and drainage rules.
Good to know: We could not confirm a clear Wyoming rule for yard runoff between neighbors; the Wyoming Supreme Court has treated misdirected irrigation water as a reasonable-care question, so talk to a Wyoming attorney about a dispute. State construction stormwater coverage starts at 1 acre.

Sources: caselaw.findlaw.com · deq.wyoming.gov

Frequently Asked Questions

Can my neighbor drain water onto my property?

It depends on whether it’s natural runoff or something your neighbor changed. In the 16 civil law (natural flow) states, the lower lot generally has to accept water that naturally flows onto it. In some states, blocking that natural flow can make the lower owner liable too. What can make a neighbor liable is a change: depending on the state, sending water onto your land unreasonably or carelessly, or collecting, concentrating or diverting it onto you, and causing damage. Find your state’s rule above.

Who is responsible for water runoff between neighbors?

It depends on your state’s rule and the facts. Courts generally ask whether someone changed the natural drainage and, depending on the state, whether the change was reasonable or careful, whether it collected, concentrated or diverted water onto the neighbor, and whether it caused damage. Deadlines to sue can be short: the Texas Supreme Court applied a two-year deadline in 2026, and Maine requires a nuisance claim within 3 years.

Do I need a permit to regrade my yard?

It depends on how much ground you disturb and where. A construction stormwater permit is required at 1 acre of disturbance in every state, and for smaller sites that are part of a larger development. Six states and D.C. require an erosion and sediment control plan statewide for smaller jobs, such as 5,000 sq ft in Pennsylvania, Delaware and Maryland, and more than 50 sq ft in D.C. Work in or near a stream, wetland, floodplain or the coast can need a state or local permit at any size. Your town or county may require a grading, drainage or stormwater permit for a much smaller job, so check there first.

What drainage rule does Pennsylvania follow?

A modified natural-flow rule. Pennsylvania courts don’t name it; the label is ours. You’re generally not liable for rain that naturally runs downhill, and ordinary grading and building on your own lot isn’t enough by itself to make you liable. But you can be liable if you divert runoff out of its natural path, collect it with pipes, downspouts or swales and send it onto a neighbor in a concentrated flow, or unreasonably increase how much reaches them. The leading case in our entry is Youst v. Keck’s Food Service, Inc. (Pa. Super. Ct. 2014), which applies Pennsylvania Supreme Court cases going back to 1895. For permits, 5,000 sq ft or more of earth disturbance, or any amount that could drain to a High Quality or Exceptional Value stream, needs a written erosion and sediment control plan. 1 acre, or less if it’s part of a larger development, needs an NPDES construction stormwater permit.

Can I be sued for runoff from my patio or downspouts?

A neighbor can bring a claim, and whether it succeeds depends on your state’s rule and the facts. Many entries name collecting, piping, concentrating or diverting water onto a neighbor as a way to become liable, and in the 21 reasonable use states a court weighs whether the change was reasonable against the harm. In Indiana, for example, you may block or redirect surface water but may not collect it and cast it in a concentrated body onto a neighbor. Whatever your state, the lower-risk setup is one that doesn’t collect water and send it onto a neighbor’s land.

Which drainage rule does my state use?

Find your state above. In our data, 21 states use reasonable use, 16 a civil law (natural flow) rule and 9 a modified common enemy rule. Kansas and South Dakota split the rule between towns and rural land, and we couldn’t confirm a settled rule in Arizona, Wyoming and D.C. Courts don’t always name the rule; in 12 entries the label is ours, based on the rule the courts describe.

This guide is general information, not legal advice. For a drainage dispute, talk to a lawyer licensed in your state. For a regrading job, check with your town or county and, for erosion and stormwater rules, your state environmental agency or county conservation district.

More state guides: Frost line depth · 811 dig laws · Retaining wall permits · Contractor licensing · Contractor deposit limits · Building codes · Planting zones · Mechanics lien deadlines · Workers’ comp · Frost dates · All state guides · Free calculators

Last checked November 1, 2026 against court opinions, state statutes and regulations, and state environmental agency and EPA pages. Entries marked “Secondary source” rest partly on older or lower-court cases. Spot something out of date? Email info@muthlerlandscaping.com and we’ll fix it.

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<a href="https://muthlerlandscaping.com/state-guides/drainage-laws/">Drainage Laws by State: Neighbor Runoff Rules and Stormwater Permits</a> (Muthler Landscaping & Construction)

Cite as: Muthler Landscaping & Construction, “Drainage Laws by State: Neighbor Runoff Rules and Stormwater Permits,” https://muthlerlandscaping.com/state-guides/drainage-laws/ (last checked November 1, 2026).

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