It’s a solved problem - backflow prevention devices will not let water from one user to flow to others, with inspections, etc there is no issue. Want recycled water? Pay for inspections and protective devices. Business users have been doing this for years.
A given property has one potable water entry point - the water meter. So no, it’s not one bad apple and all get bad water. Also, there is no regulation here, just fear of liability by water boards.
