Utility Allocation if No Sub-Meters

[Justin Spillers]

Hello, I have a 7-unit apartment complex and currently the water and sewage are not sub-metered per unit, we get one bill for the whole building without a breakdown. Can I legally require each tenant to pay for a share of the total bill or is it not possible to arbitrarily divide a bill up and charge i back to my 7 tenants?

Thanks!