Lot "A" and "B" are on a slope with "A" uphill from "B". To level the yard Lot "A" builds a brick retaining wall 19" tall on the property line of "A" and "B". "A" then fills the area with dirt and plants trees, shrubs, and grass. Water freely flows from the base and under B's driveway to the point that over time it needs total replacement. "A" claims that it was B's responsibility to provide proper draining for A's runoff. B's home was built two years prior to "A". What is the ruling in King County?
The general rule for surface water is called the "Common Enemy Doctrine" which basically provides that landowners need to "defend" their own property from surface water and that, generally, an adjoining landowner will not be liable for surface water runoff that flows onto a neighbor's property. There are some exceptions to this rule, however. One exception provides that an uphill landowner cannot collect water in an artificial channel, then discharge it on adjoining lands. Another exception is referred to as the "due care exception," which reflects a weakening of the strict applicability of the Common Enemy Doctrine, and requires a landowner, when developing property and disposing of unwanted surface water, to act in good faith and with "due care" to avoid unnecessary damage to the property of others.
You should contact an attorney to discuss your case in detail to see if any of the possible exceptions apply to your situation. Good luck.