I found a seemingly good article about removing the stuff. It is geared for brewing beer, but has good examples about how long it takes to reduce it to a level where microbes will thrive.
Removing Chloramines from water I personally don't drink it, but many fear an amoeba or microbe that can kill them so they rather have a little chemical in their drinking water. I have heard a few people around here even say they preferred using chloramine water with their animals because it was safer. I think my chickens generally let it sit long enough that it loses the scent.
Rainwater is preferable, but having chloramine water does not have to stop you from getting started brewing.