I've been to a few islands that must import bottled drinking water. The citizens themselves do, not the government.
I actually got stuck on one such island once, for one night with my then-twelve-year-old. First thing we did after securing a place to sleep, was acquire water.
If we invert it to the actual reality (many places have unsafe drinking water), then we get "the right to avoid being poisoned by your government".
It sounds obvious to me that that should already be the case.
But I don't know much about water treatment. Maybe it isn't always feasible?
Do people just have to drink bottled water in some places? Or get reverse osmosis filters?