Chlorine is a necessary evil when it comes to having mains water
piped into our homes but you may be surprised that the Chlorine
in mains water (we will call it that) is different to what we
would find in a swimming pool.  The substance injected into our
mains water is a gas not a liquid, it is commonly referred to as
chlorine by all even the water authorities but it is in fact
hypochlorous acid (true chlorine), the chlorine in swimming
pools is usually sodium or calcium hypochlorite.  When
hypochlorite (swimming pool chlorine) solutions are placed into
water the atoms hydrolyse from the molecules releasing
hypochlorous acid (true chlorine), also released are compounds
like trichloro-s-traizinetrione and sodium dichloro-s-
triazinetrione and that is why they smell similar but most of
the smell in both mains water and pools is a by-product which
are commonly refered to as total trihalomethanes and
trichloroethylenes which are created when the chlorine binds
with organic compounds in the water, all trihalomethan