Public water supplies, especially those fed by surface water, will sometimes use Chloramines as the disinfectant. These chemical compounds are a mixture of chlorine and ammonia. A public water supply might switch to chloramines because they are attempting to reduce their disinfection by-products, which are carcinogens that are created when disinfectants mix with organic matter, mostly from surface water supplies like reservoirs.
Chloramines are considered safe to drink but many people prefer to remove them prior to drinking. Certain water using applications may be less tolerant of chloramines, so some people prefer to remove them prior to creating beverages or raising fish. For brewers, water treated with chloramines for disinfection may react with phenols in malt.