I use RO water. Chlorine isn't the only problem with tap. Tap has also started being treated with a mix of ammonia and chlorine...I think it's called chloramine. It will not evaporate or dissipate and is very bad for your plants. With that said, you can have a good grow with tap but you can have an even better one with RO imo.
Chloramine
NH2Cl is commonly used in low
concentrations as a
disinfectant in
municipal water systems as an alternative to
chlorination. This application is increasing.
Chlorine (sometimes referred to as
free chlorine) is being displaced by chloramine, which is much more stable and does not dissipate from the
water before it reaches consumers. NH2Cl also has a lower, however still present, tendency to convert organic materials into
chlorocarbons such as
chloroform and
carbon tetrachloride. Such compounds have been identified as
carcinogens and in 1979 the
United States Environmental Protection Agencyā began regulating their levels in U.S. drinking water. Furthermore, water treated with chloramine lacks the distinct chlorine odour of the gaseous treatment and so has improved taste.
From Wikipedia...the most reliable source of info on the net:D.