Amazing. The pollution where I live is pretty bad so I don't use rain water. Back when I had Woodfrogs I used to use the lake water though. (Because I wasn't sure which minerals/chemicals they did/didn't need.)
I used spring water, OR I boil regular water, OR I treat it with a solution to rid of it chlorine. Lately it's just been spring water but I've used all of those methods with little problem.