That didn't sound right...
I mean that I'm not sure what would happen to your tank with tap water. Mine, for some reason, does better with tap than it did with RODI. My tap water is usable though. Some municipal water sources are safe for you and I to drink but it can contain minerals that are not good for your aquarium resulting in Dinos, Cyano, algae blooms etc. Also, some municipalities use chloramines for disinfecting the water. Those should be removed from your water source, at a minimum, using a tap water conditioner according to most sources.
I've never used water with chloramines so I can only pass on what I've been told by experts.
What I will say is I dose Ammonium and others dose Ammonia. Also, reef salt actually contains chlorine... I forget the ratio but seawater is a natural source of chlorine. In fact, read Tropic Marine Pro-Reef salt ingredients:
And chloramines are what? Chlorine mixed with ammonia - the super disinfectant. So, if we are adding chlorine to our tanks via our salt mixes and we're dosing ammonia (or it is being added naturally through waste) aren't we, in essence, creating chloramines in our aquariums?