The only way that you can accurately and fairly bill your tenants for water usage when you only have one main water meter is to add sub-meters. Those meters need to be placed in the proper location(s) in the plumbing system in order to record the usage of each tenant correctly.
Once the meters are installed, you will need to regularly read them to gather the data you need to split your bill.
There are several ways to do this:
Read each meter's register manually at the point of installation then subtract the last reading of each meter.
Read then reset a digital display that is attached to the meter by wire and can be located somewhat remotely.
Buy an online water meter reading system from Flows.com so you can access all meter readings from anywhere at any time!
In addition to allowing access to meter readings you can get scheduled reports and leak, burst, and freeze alerts.
Use this interactive tool to calculate the bill amounts for each water sub-meter
For more information about the remote water meter reading systems from Flows.com please visit this page.