If it is not separately metered then you can implement a RUBS (basically splitting the bill based on usage of each unit due to occupancy, size and fixtures).

If the owner wants to require the tenant to pay for the utilities, that can be arranged by the tenant establishing their own accounts with the utility companies, or the owner billing the tenant for the usage.

Where is he parking, is he making himself too much "at home" and leaving personal items there, receiving mail at that address, has his own key, is there when the tenants are not, causes extra wear and tear, causes an uptick in utility usage, etc. 

But keep in mind water usage and cost can vary greatly from state to state and county to county.

Not to mention that marketing, customer service, property management, owner usage, etc heavily impact each property individually. 

Also the number of bedrooms and bathrooms in the home/unit will influence the water usage to some degree. 

You could try to come up with a way to keep the bill in your name as you suggested and rebill the tenant, but that seems extremely complicated since the price varies hourly depending on peak usage rates. 

And you or your manager will have to deal with tenant conflicts over inappropriate parking.

If they respond inappropriately we will be giving them notice and finding a new company, which we might do anyway.   

Why are you monitoring your tenants AC usage and analyzing it against the outside temps?