Chloramine

Recently, municipalities around the world have begun to use
chloramine (a mixture of chlorine and ammonia) to disinfect water. This
is done to reduce free chlorine’s ability to combine with organic matter
in the water thereby producing potentially harmful trihalomethanes, or
THMs. Because chloramine has less disinfecting ability than free chlorine,
a higher concentration of chlorine is usually used to get the same bacteria
kill rate. Yet chloramine’s harmful effects are the same
as pure chlorine, so the hazards while showering are greater.