If you are referring to tap water, some people use it but some people recommend using spring or distilled water. I've only owned geckos for 3-4 weeks now, and my geckos are acting/eating strangely (atleat to my amateur mind). I hope it isn't tap water causing it, but alot of people use it. So..idk. If you are concerned, atleast step up to distilled/spring water.
I've been using tap water for decades with all of my pets not just reptiles except my male betta, of course and have no problems with it. Then again, i heard US/UK tap water is very hard water and highly chlorinated
I drink it straight from the tap and so do all of my animals. If I move back to a place with nervous making water or to a house that has a well (that water is just nasty metallic!) I can guarantee we'll all be drinking bottled water.
I use bottled spring water (some times drinking or purified water) conditioned with ZooMed reptile conditioner. It's got vitamins and minerals in it, so I figure why not. The only ones in this house that get our nasty tap water is the fish, and I have high end, remove-all water conditioner to make it safe (that I dose at 3x over).