Normal natural run-off is not illegal from one property to another in California. Adding run-off beyond what nature provides for is however a violation. This is similar in most if not all states. For example, I was disallowed to build an above ground pool in Illinois because it would remove a large amount of natural drainage from my yard and force run-off from my property to my neighbors. (I had contacted the zoning board in advance btw, the neighbors did not even know.)
While it seems petty, the neighbor is correct that this is disallowed, and while you could contact an attorney, I suggest changing the water disposal method. The latter is easier and far less costly no matter what the result.
While it seems petty, the neighbor is correct that this is disallowed, and while you could contact an attorney, I suggest changing the water disposal method. The latter is easier and far less costly no matter what the result.