At where I live, trading water is forbidden. We rent appartments and we must not have any profit on the water. Usually, the consumption is separated per person,

At where I live, trading water is forbidden. We rent appartments and we must not have any profit on the water. Usually, the consumption is separated per person, but sometimes that is not possible (when there are stores, for instance). For an odd reason, however, flat rate is acceptable, so you can charge tenants a fixed monthly fee and make an actual profit out of it. Sure, there's a risk you set the flat rate price wrong.