As far as I know, most of the resorts on sandy beach use city water and city sewer. Most have a large water tank on property to have a nice reserve in case the city supply goes down for a day or two.
Generally you get what you pay for. Discount medicine, human or animal, usually results in discount results. Just beware when you buy anything in Mexico.
Pretty sure when you pay those high prices for a rental in Rocky Point, water is included. In other words, they city is already making money to resolve the water issue and is not using it for that purpose.
That's one of the perks of living in a 'rich' country. We waste lots and lots of other things besides water.
P.S. Water is never really 'gone'. In goes back into the earth and we continually reuse it.