You're making a lot of assumptions. The gray water was "probably just" shower and washer run off, the water was "most likley" healthier,
While I doubt anyone is dumping effluant on the ground or gray water next to a potable water source, by not making sure waste water and potable water don't mix, you run the risk of contamination.
I'm aware propane tanks have a shut off at the tank, suppose the tank is on the other side of the property? My gas line has a shut off at the meter, also one at the furnace, and the hot water tank, and the fireplace. It's at least prudent to be able to isolate componants in a fuel train, and if you run a business then the fire code requires it.
Basic sanitary guidelines apply no matter where you live and exhist for the well being of everyone involved, resident and guest. It's not "government interferance" to require business's to contain their waste and follow legal requirements for building wiring, fire prevention and water supplies.