Including utilities in duplex with shared meter

[Joe Edwards-Hoff]

So, I'm looking to rent out my primary home as a duplex. I was told that it was once rented as a duplex before. I'll have to figure out a few things, but the biggest issue is shared utilities. I figured that I would just include them in the rent and then raise the rent accordingly. I also figured that I would include in the lease that the rental price will be reevaluated every X months in case the utilities fluctuate dramatically.  

I had thought about capping the utility cost at a certain amount and then dividing it up amongst the renters, but I also thought it might create issues if one renter tried hard to keep the bill low and the other didnt. That might not be worth the headache. 

Any other thoughts or suggestions?