As many of the citizens of California might have experienced first-hand, runoff water can be devastating to a house. Moreover, if a homeowner's property was damaged as a result of runoff water coming from the neighbor's land, disputes are bound to arise. That being said, it is worth bearing in mind that the law will consider neighbors legally liable for the damages only when they have landscaped their land and this alteration has influenced the path of the runoff water.
With that said, an individual looking for restitution from their neighbor for damaged property has three types of laws with which to tackle this neighbor dispute. The Reasonable Use Rule, a law followed by a majority of states, requires the aggrieved to show that the alterations carried out by their neighbor were unreasonable and that these alterations are directly to blame for the increased flow of water onto the damaged property.
The second is the Common Enemy Rule, which considers rainwater a common enemy that all landowners must face. Accordingly, each landowner is responsible for protecting their land to the best of their ability against runoff water. Even though many states adopt this rule, most of them have modified it so as to allow people to hold their neighbors liable if the alteration can be shown to have been negligent.
Alternatively, there is the Civil Law Rule, a law that holds any landowner liable should they change the natural flow of the water across the land, damaging the adjacent property in the process. However, just as with the Common Enemy Rule, there is a modified Civil Law Rule, one that allows people to alter their lands so long as these alterations are reasonable.
There are still more questions to answer in these cases, including those of compensation rights. As a result, it might be advisable to reach out to an attorney who may be able to explain legal options.