Tap water will be fine. I'm sure that almost all of us use tap water for our animals. Using filtered water or store bought water is just a waste of money for an animal that will do just fine with tap.
I've come across tap water that wreaks of sulfer too. If this is the case for you, you may want to steer clear of tap water. My uncle's tap water used to be horrible and it sucked to even wash your hands in it.
If you're using well water then it should be fine right away. If you're using city water then you might want to let it sit out for awhile to let the chlorine and such evaporate. I use city and I just fill up a gallon water jug and let it sit with the cap off overnight