Im not exactly sure how your water bill is broken down but, mine is like sostoudt's bill, the vast majority of the bill is in service charges and fee's, the actual water I use cost me about 12 bucks a month, that includes all the water I use plus the 80g p/week in water changes. Make your dad an offer, i.e. mow/rake the yard or keep the trash policed up and taken out in exchange for you doing the WC regime that you like. Or offer to spot him a fair ammount of money based on the gallons per month that you use.