But the real question is how much of a hit to the microbes and is it enough to offest the amount of money and time being spent to remove the chlorine? Even if it were cost effective to do it for a large commercial operation it just doesn't matter for a smaller indoor grow. I used to use nothing but RO filtered water, until over a year ago when I got tired of all the waste water it produced, and I have seen absolutely zero difference with my plants. The only major difference I saw was that I didn't have to supplement nearly as much Cal Mag when I went back to straight tap water.