Storm Water in Pennsylvania – Giving is Better Than Receiving


As Springtime arrives, along with warmth, al fresco dining, and as the turn from gray to green begins, so too arrives rain and its companion, storm water.  Understanding the essentials of storm water is a “must know” for any land owner.*

The Common Enemy Rule – An Upper Landowner’s Right to Discharge

Pennsylvania common law has long recognized the right of an upper landowner to discharge onto the land of another surface waters flowing on or over the owner’s land through a natural water course.  Since the mid-1800s, the Pennsylvania Supreme Court has held that, essentially, that because water flows downward, the owner of the upper land has an easement over the land of the lower owner to discharge all water that may flow or fall upon the upper lot.  But, the right of an upper landowner’s to discharge water on the lower land of his neighbor is not unlimited.  Generally, this right to discharge is only for the water’s natural courses, quantities and concentrations.  Of course, the lower landowner must accept the water lawfully discharged by the upper landowner.  This concept is broadly known as the “common enemy rule.”

Exceptions to Right of Discharge

The right to discharge is not unlimited.  To establish liability for unlawful discharge, a plaintiff need only show that a landowner collected and/or concentrated surface water from its natural channel through an artificial medium and discharged the water onto the plaintiff’s property in an increased volume or force, however, slight.

An upper landowner’s right of flowage is generally subject to two exceptions.

First, the upper landowner may not “alter the natural flow” through concentration, even if the water ultimately discharged is no greater in quantity.  As an example, an upper landowner’s construction of a series of pipes or ditches collecting quantities of water to a point of discharge upon the lower landowner’s land exceeds the rights of the upper landowner.

Second, the upper landowner may not “unreasonably or unnecessarily” change the quality or quantity of the water discharged on the lower land.  An example here, land development that redirects, concentrates, or changes the water flowing onto lower land could cause liability to the upper landowner.  This potential liability is of course balanced by reasonable development of the land in accordance with municipal and state regulations.

To impose liability on an upper landowner for the effects of surface water runoff on a lower-lying property, the lower landowner must generally show one of these two exceptions applies—that the upper landowner either “diverted the water from its natural channel by artificial means, or . . . unreasonably or unnecessarily increased the quantity (or changed the quality) of water discharged upon his neighbor.”

Limited Exceptions to Liability

Even where it is proven that the upper landowner has changed the land such that a change of the natural flow of the water occurs, or concentrates the water at a particular point, or by increasing the water’s volume, the upper landowner may avoid liability if it is shown that the use that inflicted the damage was “natural, proper, and free from negligence, and the damage unavoidable.” It is a long recognized principle that all landowners have a right to the use and enjoyment of their own property, and if in exercising that right, without negligence, an unavoidable loss occurs to the lower land owner, then, the law will treat this as a “loss without injury.”  For this liability exception to apply, the upper landowner must show that “the damage was necessary and unavoidable” and that it could not be prevented by reasonable care.

Pennsylvania Storm Water Management Act

Many municipalities have adopted storm water ordinances or other applicable regulations.  Additionally, the Commonwealth of Pennsylvania enacted the Storm Water Management Act (“Act”).  The Act does not change or supersede the common law rights, obligations and remedies as between an upper and lower land owner, nor is the common enemy rule impacted.  Pertinent to a general understanding of storm water law in Pennsylvania, as between landowners, the Act provides:

Any landowner and any person engaged in the alteration or development of land which may affect storm water runoff characteristics shall implement such measures consistent with the provisions of the applicable watershed storm water plan as are reasonably necessary to prevent injury to health, safety or other property. Such measures shall include such actions as are required:

(1) to assure that the maximum rate of storm water runoff is no greater after development than prior to development activities; or

(2) to manage the quantity, velocity and direction of resulting storm water runoff in a manner which otherwise adequately protects health and property from possible injury.

Storm Water Management Act, 32 P.S. § 680.13.  However, subsequent case law has held that neither landowners nor state and local governmental entities could be held liable under the Act for flooding incidents impacting other property owners that occurred before the county adopted its watershed storm water plan because a prerequisite for a violation of the Act was the existence of such a plan.  See Lincoln Investors, L.P. v. King, 152 A.3d 382 (Pa. Commw. Ct. 2016).

Certain political subdivisions may also be liable under the Act.


Storm water remains the “common enemy” as between landowners.  As land development overtakes natural open space, and suburban sprawl and redevelopment changes the natural, or existing, flow, course and concentration of water, storm water rights, remedies and regulation have become increasingly utilized.  Further, with what appears to be an increase in drastic rain and storm events, storm water run-off is amplified and so are its effects and potential damage.  Re-configured roadways and private drives, railroads, damaged creeks and detention basins, have all been the subject of litigation, in addition to claims arising simply from the development of raw land, or the re-development of an existing site with unplanned, or under-planned, for storm water results.

Flooding the land of another with increased flow, or collected, re-channeled water, is prohibited; likewise, also prohibited is a lower land owner damming, or blocking, acceptance of a permitted flow of water from an upper land owner.

If you have a question concerning storm water, please contact Eric B. Smith, Esquire, 215.540.2653 or

Mr. Smith has been consistently recognized by Super Lawyers and Best Attorneys and served as President of the Montgomery Bar Association in 2017.  For more information about Mr. Smith, please click here.

*This article does not address the breach, alteration or enforcement of express storm water easements.

Published March 17, 2021