Multifamily - utilities not separated

[Melissa Steinour]

Hi - I just purchased an under/over duplex. Unfortunately the natural gas and the borough water/sewer/trash is not separated.   Therefore, I have to do my best to divide the bills as fairly as possible.   Would it be best to build these expenses into the rent (making the rents look a little higher than market value) or can I still bill my tenants monthly for gas and quarterly for the W/S/T even though I can't produce a "bill" for them to see for their particular sides usage?  

I would appreciate any advice on this...