How to charge for utilities when property online has one meter?

[Joe Frey]

I just purchased a property that was a duplex at one time and I'm converting it back to rent to two tenants. What are some good ways to bill/charge for a property that isn't metered for each individual unit? Should I just include utilities in the cost of rent? If so, how should I go about determining what to charge? 

[Kim Bayless]

You could even have a clause in the lease for deliberately wasting use, as in the open window case above! I don't because it's a condo and I haven't had issues.