Flooding, surface runoff, and even leaking sprinklers can spark disputes between neighbors.

When water causes property damage -- flooded basements, collapsing retaining walls, or soggy gardens, for example -- feuds between neighbors often result. But the legal issues can be as muddy as the mess in your backyard.

Surface Water Runoff and Flooding

As a general rule, a neighbor is not liable for harm caused by the natural conditions of land. If the land lies in such a way that a particular amount of water is dumped onto your backyard every year from rain running off your next-door neighbor's property, it's not legally your neighbor's fault. But what if your neighbor landscapes his property so that the amount of water running onto your yard doubles every year? Your neighbor would say that the change is still caused by the naturally occurring rain, not his landscaping. But you would probably prefer to take your neighbor's action into account. It turns out that three different rules of liability govern situations like this.

The reasonableness rule. In a majority of states, when one neighbor alters the land and damage occurs to another, the neighbor is liable for the damage if the alteration was "unreasonable." If you sue a neighbor over damage you've suffered, judges will want proof that the neighbor did something unreasonable that altered the natural condition and caused your harm.

The "common enemy" rule: Lower landowners beware. In the past, many courts treated excessive rainwater as a "common enemy," damaging property at random. Under this theory, you were expected to take measures to protect your own property from water coursing across the land. Even if one neighbor who lived on higher ground diverted water to prevent flooding and deposited it on you, you were expected to protect yourself from the extra water.

Fortunately for lower landowners, the handful of states that still follow the common enemy rule -- including Montana, New York, and the District of Columbia -- have modified it. These states allow a property owner to divert vagrant surface water only if the work is not unusual or extraordinary and if the property owner uses reasonable care to avoid damaging adjoining property.

The "civil law" rule: Upper landowners beware. A number of states follow a rule which is, in theory, the opposite of the common enemy rule. The civil law rule holds that if a person alters the natural flow of surface waters in any way that harms the use and enjoyment of another property, that person will be liable for that harm. Unlike the common enemy rule, which requires lower landowners to fend for themselves, the civil law rule holds upper landowners liable for any detrimental changes in runoff patterns.

Like the common enemy rule, however, states no longer apply this rule in its strictest form. States have developed modifications and exceptions and now often judge the behavior of both parties before saddling the upper landowner with the bill. California, for example, expects that both parties will act reasonably, which includes the duty of the lower landowner to take protective steps.

Water Damage Caused by Carelessness

If your neighbor acts unreasonably or carelessly with water on his own property in a way that causes water damage to your property, you can sue for compensation for your losses and also ask the court to order the neighbor to stop the action.

Common culprits of this type of water damage include garden hoses or sprinklers left running too long and water pipes that get clogged, get old, leak, crack, or freeze. Owners are responsible for their pipes and for damage they may cause, even if the pipe just wears out or freezes in cold weather. Tree roots, including roots from neighboring property, can also damage pipes. Just as property owners are responsible for damage caused by their broken pipes, tree owners may be responsible for damage caused to another's property by their tree's branches or roots.