As for the original question. I have well water. The snakes drink it, soak in it, and dump it over to mess up the cage.
My friends who have snakes have city water. The snakes drink that, soak in it, and dump it over in THEIR cages. The herp store locally, uses city water.
I've never seen anything to prove to me that typical water bothers any snake, no matter what type it is. You could give it purified evian if you want to. Some people will probably claim ONLY purified water, but IMHO, if it's pure enough for me, it's fine for the snakes.