It depends on where you live and what's in the water. I do not use tap water because my city fluoridates and fluoride is a problem for chameleons. You can contact your local water authority (or look at their website) to get information on the water in your area. If in doubt, it's probably safest to use purified or reverse osmosis filtered water. Note that a "brita" type filter does not remove fluoride or anything harmful, it just removes things that taste bad...you are not concerned with taste.