Oh, leaving water to evaporate overnight is different than "distilling it"-which typically requires something to boil in (heat is usually used to speed up the process), cooling coils for condensation, then the collected water is called distilled. Leaving water in an open container overnight isn't distillation and is not going to remove minerals, heavy metals, etc., though chlorine will dissipate from the solution. But I'm splitting hairs I suppose. If your water is safe to drink, it is almost surely safe for your reptiles to drink. 3 simple liquid test kits can tell you a lot about your water, or since you won't need it more than once, ask a local fish store what they'd charge to test the pH, KH, and GH. Heck, a call to one good local fish store would probably tell you everything you need to know about your municipal tap water.