My kin in CA would never drink tap water. It’s that nasty. I bet they’d appreciate a reservoir of fresh water.
Well, California is 164,000 square miles, so I’d suggest your relatives’ experience may not be representative. Lake County, for example, is very geologically active and the water is super hard. You wouldn’t drink it on a bet. But the snowpack components of those tens of trillions of gallons of precipitation we got is definitionally pure as the driven snow. My community gets is water from Folsom Lake, and you wouldn’t have the slightest objection to its taste
The aircraft industry in Southern California used a lot of trichloroethylene for parts cleaning back in the day. After it was used and became dirty they just dumped it, sometimes into old water wells. From there it kind of spread out through the area ground water. Trichlor causes kidney cancer.