If it's safe for people, it's safe for geckos.
If you were really worried about it and have gross tap water, you could buy cheap bottled water for them, but I wouldn't go adding chemicals to normal tap water.
I actually use bottled water (just cheap stuff) for all my snakes as I read that the chemicals that get put in our drinking water can be detremental to them, (and yet I drink it by the litre!) I haven't actually heard of putting anything in to get rid of the chlorine though.
if your really worried about the chlorine in normal water just run a bucket the night befor
if you leave water for 12-18 hrs all of the chlorine will have dissapated and will not be an issue
other way you can go is get a small water tank (goverment rebates still apply in most states) but you must make sure that it stays clean and nothing can get in and die or this will turn your water VERY quickly.
Or a simple cheap benchtop water purifier will do exactly what you need without continually having to pay $$$ for bottled water
we are on tank and bore so no chemicals in it ,,,,,,,,,,,but there are days that the bore stinks like rotten eggs .........lucky we dont absorb the smell