The common enemy rule applies in surface water cases in Pennsylvania.
The common enemy rule is the general principle that the law regards surface waters as a common enemy which every proprietor must fight to get rid of as best he may.
Rights of Upper Land OwnersThe owner of upper land has the right to have surface waters flowing on or over his land discharged through a natural water course onto the land of another. He may make proper and profitable use of his land even though such use may result in some change in quality or quantity of the water flowing to the lower land.
When upper landowners are liable for the effects of surface water running off their propertyUnder the common enemy rule, an upper landowner is liable for the effects of surface water running off his property in two distinct circumstances:
(1) where the landowner has diverted the water from its natural channel by artificial means; or,
(2) where the landowner has unreasonably or unnecessarily increased the quantity or changed the quality of water discharged upon his neighbor.
Bretz v. Cent. Bucks Sch. Dist., 86 A.3d 306, 315-316 (Pa. Commw. 2014).
Regarding the first exception to the common enemy ruleRegarding the first of these two exceptions to the common enemy rule, "the determination of whether a landowner `has diverted the water from its natural channel by artificial means' does not involve consideration of the reasonableness of the change in quantity or location of water flowing onto the lower land.
Rather, to establish liability, a plaintiff need only show that a landowner collected and/or concentrated surface water from its natural channel through an artificial medium and that the water was discharged onto the plaintiff's property in an increased volume or force, however, slight." Bretz at 316.
In other words, when determining whether a landowner has diverted water from its natural channel by artificial means, "the legal wrong lies in the artificial diversion or collection of water itself . . . without regard to the degree in which the volume or force is increased. A plaintiff need only show that a landowner collected and/or concentrated surface water from its natural channel through an artificial medium, and the water was discharged onto the plaintiff's property in an increased volume or force, however slight." Id. at 316.
Upper landowners do "have a right to have surface waters that run across [their] propert[ies] discharge[d] through a natural watercourse onto the [Plaintiffs'] property." However, they do "not have a right to `turn the water from what would be a natural channel to an unnatural channel where the water would not normally flow' or to `increase or change the concentration of the water by artificial means.'" In this regard, the questions of what is a "natural channel" and what is "reasonable" are issues to be determined by a jury.
Youst v. Keck's Food Serv., 94 A.3d 1057, 1073-74 (Pa. Super. 2014); id. at 1068.