RO/DI treatment is a hedge against tap water which typically has impurities that can cause issues in our aquariumsQuestionI’ve been keeping saltwater aquariums for five years, and in all that time I’ve never used RO/DI water for top offs or mixing up clean salt water. I just use tap water treated with a dechlorinator / dechloraminator, and I’ve never had any problems. Could it be that people are exaggerating the benefits of using RO/DI?” – Submitted by Lee H. Answer Though you may have gotten by using only a dechlorinator/dechloraminator to treat your water thus far, you may not always be so lucky. I’m a strong proponent of using RO/DI-treated (or otherwise purified) source water in any marine aquarium system for several reasons. Here are just a few: Water treatment protocols are for people Municipalities aren’t (nor should they be) worried about providing water that’s safe for sustaining sensitive marine organisms. Their only concern is ensuring that the water is safe for people to drink, bathe in, etc.