Being charged 18 times for water - 18 unit building with 1 meter

[Darryl Good]

Hello All, Just purchased an 18 unit multi family.

The water billing for the town charges a flat sewer fee ( x18 - $422) and flat water fee (x18 - $254) plus they meter the water usage as well. ($180

In my mind Since there is only one meter, I believe i should be charged 1 flat sewer fee and 1 flat water fee and of course the amount for all the metered water we use.

Has anyone gone through this with a city? 

What is an average water usage $ per unit/per month?

Thanks so much!