I have read that higher levels of chlorine can kill or at least slow the growth of mycorrhizal networks in soil atmospheres. I have no legit studies to back that up or any way of knowing what levels are considered dangerous. It makes sense but I don't think we're dealing with those kind of levels out of tap water. If you're concerned the best answer is to allow the water to sit overnight or give it some good aeration for a couple hours. Squidbilly brings up the very thing we as growers need to be aware of when we're talking about tap water- CHLORAMINE. This is sometimes used in drinking water as a replacement for Chlorine. It doesn't evaporate and is more effective in disinfecting a water supply so it's considered a cost saver. Problem is, it also increase the likelihood of being exposed to other contaminants in the water supply such as lead. As an avid home distiller I'm always concerned about Chloramine because it most definitely will cause an off taste in a quality distillate. Simple cure for this: crush up a couple Vitamin C tablets and add them to your water before using. This will completely dissipate the choramine with no fear of it returning. Don't use ascorbic acid as it's only a temporary fix, Vitamin C works permanently.