Dispersing the Water bill

[Miles Peck]

I have 25 units in West Burlington Iowa. The units are split up between 3 separate buildings. Each building has 1 water meter. I have been paying each water bill since I have owned the apartments. I would like to find a way to make that part of the tenants responsibility. I know it is possible to just put in multiple city water meters, but I think that would be expensive. How do I charge the tenants for water when I don’t know how much each unit is using? Thanks for any feedback.