In, Massachusetts, you are not allowed to charge the tenant for the cost of the water unless the water is seperately metered and water saving devices are installed. The tenant can also be charged for the heating of the water (via a gas/electric bill) and only if it is on a separately metered circuit from any other tenant or common area and is stipulated in the lease. This deduction by your landlord should not have taken place unless the charge was listed in your lease, and if he continues to refuse to return it, you may have to take him to small claims court. They may award you up to 3 times damages for his refusal to do so.