Separating water line on a duplex?

[Ming O.]

We are closing on a legal duplex where we will be living in the main house and renting out the back house. The back house has separate gas and electric lines, but we're debating on adding a water line. 

The cost will be hefty - $3600 just for the city to put it in at the street level, and who knows how much it would be to connect from the street to the house (not sure about that process). Since the back house is currently empty, this would be the time to do it. I feel strongly that the tenant should be responsible for his/her water use, especially with the drought situation. We plan on holding onto the property for a long time, and figure it would pay off in maybe 7 years or so? It would be tight, but we do have some money to do this now. Even though most landlords here pay the water, the rental market is very competitive in our area, and I believe we could get a tenant to agree to pay for the water, albeit maybe having to lower the rent slightly.

What is your opinion on this?

Thanks!