Submeter v.s. Flat fee (water/sewage)

[Niyi Adewole]

Good Evening Everyone, I am closing on my first tri-plex early next month, and i am looking for a way to pass the water/sewage cost to the tenants. I called a few sub-metering companies, and the best price i recieved was a one time charge of $1500 to install the 3 meters, and a monthly reoccurring charge of $50 to read the meters each month. 
The $50 per month would be passed to the tenants, but my question is; is sub-metering worth the cost? Or would you simply charge a flat fee each month for water/sewage? (Gas and electric is already separately metered) Any and all advice is welcome