Sub metering water on a duplex

[Connor Mullen]

I have a duplex under contract right now, the current owner pays for the water. The water bill averages around $150/month, absolutely killing cashflow on this property.

So as a result, I'm planning on sub metering the water and sewer lines. The city is going to charge $600 to add a new line and upgrade the existing or they will charge $1200 to just add a new line for the one side. I'm not sure what the contractor pricing will be just yet, as I haven't gotten pricing back from them.

Is sub metering the best idea? Should I bill the tenants a flat rate per month? Or are there other options out there?