Drainage law

The common enemy doctrine is a rule derived from English common law. It holds that since surface water is a "common enemy" to landowners, each landowner has the right to alter the drainage pattern of his land (for example by building dikes or drainage channels) without regard for the effects on neighboring parcels, as long as that water flows to where it otherwise would have naturally flowed. Typically, a landowner can capture surface water (e.g. by rain barrels or dams) as well, and lower landowners will not have a cause of action unless the diversion is malicious.[2] This rule is followed by approximately half the U.S. states, although some states have modified the doctrine to hold landowners liable for negligent damage to the parcels belonging to neighboring landowners.

The civil law rule (so named because it is derived from the civil law systems of France and Spain) is effectively the opposite of the common enemy doctrine. It holds that the owner of a lower parcel of land must accept the natural drainage from those parcels above his, and cannot alter the drainage pattern of his own land to increase the drainage flow onto parcels lower than his own. For this reason, this rule is sometimes referred to as the "natural flow rule".

Application of the civil law rule in its purest form would inhibit the development of land, since virtually every improvement on a parcel would alter the natural drainage. For this reason, this rule has been modified in those jurisdictions that use it, to permit reasonable changes in natural flow, often weighing the competing interests of neighboring landholders with the benefit of the development of the parcel.

The reasonable use rule presents an alternative to both the common enemy doctrine and the civil law rule. It allows a landowner to make "reasonable" alteration to the drainage pattern of his parcel, with liability only occurring when the alteration causes "unreasonable" harm toward neighboring parcels. Judicial mitigation of the common enemy doctrine and civil law rule often results in an approximation of the reasonable use rule.[2]

Because the reasonable use rule presents a subjective standard, courts will often employ a balancing test to determine whether a landowner is liable to neighbors for alteration of drainage. For example, under the Restatement of Torts, the test was:

1. Was there reasonable necessity for the property owner to alter the drainage to make use of their land?
2. Was the alteration done in a reasonable manner?
3. Does the utility of the actor’s conduct reasonably outweigh the gravity of harm to others?