Water is always a tricky thing and sometimes it can come down to the species of frog you have. In general though a pH that is around 7 is ideal (granted a little alkaline and/or acidic is ok), not too soft or hard. Also you wanted to do a test sample of your water to check the Chem Profile on it (ie nitrate, heavy metals, chlorine levels etc.) Usually if you have decent tap water, you can use a dechlorinator with a heavy metal remover/nitrate remover etc depending on your water. I use a dechlorinator that has a heavy metal remover in it. Works very well and my frogs are as healthy as can be. Also if it is just a small water dish that you need to fill, say for a tree frog and/or terrestrial species then you can use bottle water (be sure to pick one that has a fairly neutral pH) or just install a filter on your faucet, but be sure it is certified to remove heavy metals, nitrates, and chloramine - BE SURE THE FILTER FOR YOUR FAUCET HAS A NSF CERTIFICATION. Hope this helps!