Interesting. So even moving out of the state does not release you from having to pay water, I am surprised Power like SMECO or Washington Gas does not join the party, I think most people after a while would see owning as a very expensive waste of money..
Different set up, SMECO and Washington Gas are for profit companies (yeah, I know SMECO is a co-op) while METCOM is a governmental agency that's required by the bondholder to recover its costs to pay off the bonds. The other two pull the payments out of operating revenues/profits.
Some utilities elsewhere do have a maintenance of service charge when you disconnect your service.
I don't know specifically how METCOM is set up but its likely considered an enterprise fund which is divorced from the property taxing function of the County, so it stands alone and charges its own fees, which have to cover treatment and delivery plus all the capital costs associated with that. The bond holders set how much has to be recovered from each customer to cover the bond payments (treatment and delivery are operating costs). The old way was front foot benefit, the more frontage you have the more you pay. The new way is a flat amount for each tap holder.
An ignored part of every bond offering is that if the benefit charges don't cover the payments then general tax revenue is used to pay them.