In property law, one way that a landowner may interfere with another’s use of her land is by altering how surface water, such as rain or snow melt, drains. A landowner may build a building, pave her land, or alter the contour of the land in a way that increases the amount of surface water that drains onto neighboring property or changes where it flows, thus damaging nearby property.

Or a landowner may try to protect her property against surface water by filling in her land, causing the water to back up onto her neighbor’s land.

Different states follow different rules for resolving this type of dispute.

The reasonable use rule: Altering drainage reasonably

Many states, though probably still a minority, apply the reasonable use rule. This rule essentially applies the law of nuisance to alterations of drainage: Landowners may alter the drainage of their land as long as they don’t unreasonably interfere with others’ land.

As in nuisance cases, courts consider all the relevant circumstances to decide whether a particular alteration of drainage is unreasonable:

  • The value and importance of the plaintiff’s and defendant’s land uses that will be affected by the drainage of surface water

  • The extent to which the plaintiff’s and defendant’s land uses will be impaired by the drainage of the surface water if the other party prevails

  • Whether either or both of the parties could avoid the conflict by some other drainage method

  • Whether the defendant acted maliciously or negligently in altering the drainage

Although a minority of states has expressly adopted this rule for surface water disputes, opinions in other states seem to be moving in this direction, applying reasonableness and balancing ideas.

The common enemy rule: Protecting your own land

Some states apply the common enemy rule to surface water disputes. The simplest version of the common enemy rule is that every landowner has the right to protect herself against surface water however she chooses. Therefore, no one has a right against other landowners, and no one is liable to anyone else for causing damage by alterations to the drainage of surface water.

This rule may promote development of land by protecting landowners from liability for altering the land in ways that change surface drainage. But it also may encourage landowners to divert surface water in ways that most benefit themselves without considering how those actions affect other properties.

Courts that apply the common enemy rule therefore have often qualified and modified the absolute version of the rule. Here are some common exceptions to the general rule that someone isn’t liable to others for altering surface drainage. A landowner is liable for damage resulting from her alterations if

  • The alteration is intended to deflect surface water, as with ditches or pipes, and the alteration discharges more water or directs drainage in a way different from the natural drainage.

  • The alteration of the natural drainage is unnecessary or isn’t for a reasonable purpose.

  • The landowner alters the natural drainage carelessly or negligently.

The civil law rule: Paying for any harm you cause

In its simplest form, the civil law rule says that landowners are strictly liable for altering the natural drainage of surface water. The rule thus is the exact opposite of the common enemy rule. Landowners have no right to alter drainage, and they have the right not to be injured by others altering the drainage.

This rule may discourage development because almost any kind of development alters the natural drainage and therefore exposes the owner to liability. Of course, a developer of land can negotiate with the neighbors to buy the right to alter drainage, but that increases the cost of development.

Because the civil law rule sometimes seems undesirable, courts have made exceptions to this rule, too. Here are common exceptions:

  • The rule doesn’t apply in urban areas. In those areas, development is more desirable and appropriate, so the common enemy rule or a version of the reasonable use rule applies instead.

  • Agricultural users can alter drainage if it’s good agricultural practice and they direct the drainage through natural channels.

  • A landowner isn’t liable if she alters the natural drainage but it doesn’t do any more harm than before.