Mercury
Hg·Affects brain, kidneys, heart, reproductive
A heavy metal neurotoxin that enters water from coal combustion, mining, and industrial discharge. Methylmercury, the organic form, is one of the most toxic compounds in the environment.
Hg
EPA limit
0.002 mg/L (2 ppb), inorganic mercury
Most at risk
Pregnant women, infants and young children, residents near coal-fired plants and historic mining sites
Found in
City water · Well water · Industrial areas
AquaOx filters
YesKDF-55 + activated carbon (paired with RO for elevated mercury)
What it does to you
Health effects
Mercury is a potent neurotoxin. Methylmercury, the organic form that bacteria produce in aquatic environments, crosses the blood-brain barrier and the placenta, making prenatal exposure especially harmful to the developing nervous system. The WHO lists mercury among the top ten chemicals of major public health concern.
In adults, chronic mercury exposure damages the brain (tremors, memory loss, mood changes, peripheral neuropathy), the kidneys (it accumulates in renal tissue and impairs filtration), and is associated with elevated cardiovascular risk in long-term epidemiological studies.
Inorganic mercury, the form regulated in drinking water, is less neurotoxic than methylmercury but still damages the kidneys at chronic low doses. It also disrupts reproductive function and is linked to lower fertility and adverse pregnancy outcomes at elevated exposures.
Where it comes from
How it gets into your water
Mercury enters drinking water through a mix of natural and industrial pathways. The single largest anthropogenic source globally is coal combustion: mercury is released from burning coal, deposited from the atmosphere into surface water, and converted to methylmercury by aquatic bacteria.
Other industrial sources include chlor-alkali plants (a historic problem), gold mining and processing (especially small-scale amalgamation), medical and dental waste, and improperly disposed mercury-containing products (thermometers, fluorescent bulbs, batteries, switches). Erosion of natural mercury-bearing mineral deposits adds a baseline that's amplified in regions with historic mining.
Once in a watershed, mercury is persistent. Decades-old contamination from gold mining in California and from chlor-alkali plants on the Great Lakes still drives advisories today.
Coal-fired power plants
Largest anthropogenic source globally
Mining and smelting
Especially historic gold mining
Chlor-alkali plants and legacy industrial sites
Persistent watershed contamination
Natural mineral deposits
Cinnabar (mercury sulfide) ores
Find out for yourself
Is it in your water?
Municipal utilities test for mercury and report results in the annual Consumer Confidence Report. Most US city water is well below the 2 ppb federal limit, but utilities downstream of legacy industrial sites can run closer to the threshold.
Private well users near historic mining areas, coal-fired plants, or industrial corridors should test specifically for mercury. State health departments publish fish consumption advisories for mercury-contaminated water bodies, which is also a flag that the surrounding groundwater may carry elevated levels.
The fix
How AquaOx filters it
AquaOx's KDF-55 copper-zinc media reduces mercury through redox chemistry, converting soluble mercury ions into insoluble forms that get trapped in the filter bed. The activated carbon stage adds capacity, with sulfur-impregnated carbon being particularly effective at binding mercury.
For well sources or municipalities with documented mercury at or above the EPA limit, AquaOx recommends pairing the whole-house system with a point-of-use reverse osmosis unit at the kitchen sink. RO filters both inorganic and organic mercury to very low levels, giving you a second barrier specifically for drinking and cooking water.