Legal Question in Landlord & Tenant Law in California

California law bans "self help". You can only get the tenant out by following the three day unlawful detainer proceedings, not by getting the water turned off. If you properly served them with the three day notice, you now have to file suit for unlawful detainer and damages. You can look at a Nolo Press book to see how that is done but if you make any mistakes you can lose or have the matter delayed. There probably is a clause in your contract, if you were careful, for payment of attorney fees to the winning party, but unless they have assets how are you going to collect?

Turning off the water is self help and should not be done. There is also the question of the validity of your three day to pay or quit. If the 60-day has expired and there is no express agreement that the notice was extended, the tenants can argue that you only action is to file an unlawful detainer based upon the 60-day notice.