Help with my two family house

[James Thomas Nakashian]

I recently purchased a two family house, the person living downstairs has been there from the previous owner. The upstairs is vacant. The tenant downstairs says his utilities were included in his rent. As the new owner I have recently found a new tenant for upstairs. I would like to split the utilities between the upstairs and downstairs tenants. Unfortunately the renter downstairs has been having his utilities covered in his rent. What would be a viable solution to having the upstairs tenant and the downstairs tenant split the cost of utilities? I am trying to come up with a solution that makes both tenants happy..