Grandfathered tenants:changes in utility payments do's and don't?

[Anastasia Balaeva]

Hi to all! 

I am about to make an offer on a 4-unit property in Jacksonville, FL., but it looks like the seller has a long term tenant and a new one moving in on March 1st. The issue that I am running into is that the rent on both of these leases are well below market rate and on top of that, the water is included in the rent price. I got in touch with the utility company and it looks like the four units are on separate meters. So for the two new tenants, I would like to have them pay their own water bill. My question is, if all four tenants are living in the same property can two pay for their own utilities and two not, considering they were grandfathered in?