I have always served tap water, with no ill effects. We don't do anything special for ourselves, either. Actually, our water here tastes fine.
Not long ago, though, I read somewhere (can't remember where at the moment) that tap water should be allowed to sit for several hours, to allow the chemicals and whatnot to escape, since they are irritating to a kitty's sensitive nose. Made sense. Also, explained why it happened so often that I'd put fresh water down for them, and they'd look and sniff and then look at me as much as to say, "Well, what did you do THAT for???"
So, now I leave the water to stand in a large jug, and pour from that for them. They seem quite happy with the arrangement.
They do take a sip now and then from the faucet or the toilet (if somebody leaves the lid up
) I've even caught Fawn drinking from the basin of soapy water, when I'm washing my face.
Go figure! (She likes to supervise.)