Mercury in Drinking Water

Mercury is a naturally occurring metal that combines with other elements to form inorganic mercury compounds. Mercury also combines with carbon to make organic mercury compounds. The major source of mercury is from natural degassing of the earth's crust. The U.S. EPA has found mercury in water has the potential to cause kidney damage from short-term exposures at levels above the maximum contaminant level (MCL). No health advisories have been established for short-term exposures. However, on a chronic basis, mercury has the potential to cause kidney damage from long-term exposure at levels above the MCL. The EPA has not discovered sufficient evidence to state whether mercury in drinking water has the potential to cause cancer over a lifetime.

Contaminant  In Water As Maximum Contaminant Level

Mercury (Hg)

Metallic Mercury (Hg)
Mercuric (Hg2+)
Mercurous (Hg1+)
Methyl Mercury

MCL* = 0.002 mg/L
MCLG** = 0.002 mg/L
WHO† Guideline = 0.006 mg/L

Sources of Contaminant

Natural de-gassing of earth's crust

Combustion of fossil fuels and other industrial release 

Potential Health Effects

High levels can damage the brain, kidneys, and developing fetus.

Effects on brain functioning may result in irritability, shyness tremors

Changes in vision or hearing, and memory problems

Treatment Methods


Reverse Osmosis

GAC filters (solid block and pre-coat)

Sub-micron filters properly designed with adsorption media 

*Maximum Contaminant Level (MCL) — The highest level of a contaminant that is allowed in drinking water. MCLs are set as close to MCLGs as feasible using the best available treatment technology and taking cost into consideration. MCLs are enforceable standards.

**Maximum Contaminant Level Goal (MCLG) - The level of a contaminant in drinking water below which there is no known or expected risk to health. MCLGs allow for a margin of safety and are non-enforceable public health goals.

WHO† - World Health Organization

Click here to open WQA's Technical Fact Sheet on Mercury.

Click here to access all of WQA's Technical Fact Sheets.