I use distilled water I get 5 gallons for a little over $3. In addition to not having chemicals and being 100% safe it's also what your supposed to use in misting systems so they don't clog the tubing or nozzles
Distilled water may not be the best choice for your pet, water has minerals that your Cham needs, distilled water is lacking these making the water a tad too acidic
Distilled also has Trace amounts of copper from the distilling process. I tend to stay away from it since I used to keep reef aquariums and distilled water could kill corals. Not sure if it has any effect on champs but it's a habit of mine to avoid it lol. Is use tap water filtered through a Brita filter. Just a simple carbon based filter system so remove alot of the harsh chemicals in our tap water.