Have you ever been somewhere where the water coming from the tap isn’t clean enough to drink? It’s very dangerous, even if you drink bottled water. When we used visit family in Bangladesh in the 1990s, we’d bring along a ton of Evian. Not only would we drink it, but the kids would take sponge baths with it, because you definitely should not shower in water you wouldn’t drink. But every time one of the kids would still get sick, because it’s hard to avoid: washing your hands in tap water, eating from dishes washed in tap water, eating fruits or vegetables rinsed in tap water, etc.

The only household uses you could use a lower grade of tap water for would be toilets and clothes washing (and then only if you run the clothes on a hot cycle).