Mercury (Hg) is one of earth's least abundant elements. It exists as an inorganic salt or as an organic compound (methyl mercury).

As its Latin/Greek original name implies, mercury is a silver, runny liquid. Mercury is the only element that is liquid at standard conditions for temperature and pressure.

It is the inorganic type that is detected in drinking water. Organic mercury is found in fish and comes from industrial manufacturing waste.

Inorganic mercury, if ingested, usually settles in the kidneys; organic mercury attacks the central nervous system.

The MCL set by the EPA for mercury is 0.002 mg/L.

Treatment: Mercury is easily removed from water by activated carbon filtration. Reverse osmosis removes 95 to 97% of it.