I had a similar situation at a rental property where a neighbor was stealing water. I merely put locks on the outdoor spigots. I obtained them Any man can be a father but It takes someone special to be a Bat Dad shirt Amazon but they are available at any home center or hardware store. I have a key and the tenant has a key. Since I’ve done this my tenants water usage has returned to normal and everyone is happy except for one neighbor. That particular neighbor who is unhappy may be even unhappier in a few months. I’m in negotiations with his landlord to buy the house he is renting and I don’t like tenants who steal, and using a neighbors water without permission is theft. He may be looking for a new home at lease renewal.