Splitting out shared utilities

[Angie Y.]

Hi! I bought a home and converted the garage into an ADU. I rented out the main house already, and all utilities are in the tenant's name. I split off the electric meter for the ADU, so that will be billed separately. However, the water and gas would be prohibitively expensive to split out, so I need to figure out how to handle those utilities and bill seperately. Any suggestions on how to do this? I heard of RUBS, but not sure if that works in this case, if I can do that myself or need a vendor?