Can my landlord only charge one apt in a 3apt house for excessive water consumption if there is only one meter

My landlord pays utilities according to the lease, but it also states that if the lessee does not conserve utilities, a fee (to be based on previous invoices) will be charged to lessees. I live in a house that has 3 one bedroom apts in it (but only 1 water meter), however 2 of the apt (including mine) have 2 tenants for a total of 5 tenants. Over the weekend th landlord brought me the quarterly water bill from the 4/1/08-7/01/08 and told me and my boyfriend that we were responsible for paying the entire amount of excess between the last bill adn the current bill. We didn't even move into the house until the end of May. He claims that we are completely responsible because i had used the water hose to water the flowers i planted, however I was never told not to use the hose and it is directly beside my front door. When i try to discuss this situation my landlord refuses to talk to me, telling me to talk to his lawyer. Can I be held legally responsible for the entire amount of the bill