If you keep a sourdough starter going, you are advised to use dechlorinated water to refresh the starter. The chlorine is said to kill the beneficial bacteria you need in conjunction with the wild yeasts for a good starter.
I’ve used plain tap water in my starters with no problems, but, to be on the safe side, I use a Brita filter pitcher to remove impurities in the water. You can also leave pot of water out overnight to let the chlorine out-gas from the water.
Interesting. I did not know that.