When people hear “mercury,” they think of fish advisories and old thermometers. But mercury gets into drinking water too — and unlike the mercury in fish, the kind in water has its own treatment playbook.
What it is
Mercury is a heavy metal that exists in several forms. In drinking water, the regulated form is inorganic mercury — the kind that comes from erosion of natural deposits and industrial discharge. (The organic methylmercury that accumulates in fish is the more toxic form, but that’s a food story, not a water story.)
Where it comes from
Erosion of natural mineral deposits is the background source. On top of that: discharge from refineries and factories, runoff from landfills and croplands, and fallout from coal burning that settles into watersheds. Private wells near any of those deserve a test.
The health picture, honestly
The kidney is mercury’s primary target — it’s where the metal accumulates and does its damage. The nervous system is the other concern, especially with inhaled or organic forms. The EPA’s legal limit is 2 parts per billion (0.002 mg/L), and the health goal sits at the same level — there’s no “a little extra is fine” here.
How to test
A lab metals panel from a state-certified lab. Mercury needs specific analytical methods (it doesn’t show up on a basic test strip), so make sure the lab actually runs it. City water folks, check the annual report.
What removes it
Reverse osmosis and distillation are the EPA’s best available technologies for inorganic mercury — both highly effective. Granular activated carbon handles the organic forms. Copper-zinc filtration (KDF media) is another proven option, one New Jersey’s DEP specifically recommends for private wells. NSF-53 listed filters cover mercury.
What does NOT remove it
Boiling — and this one matters, because boiling can release certain forms of mercury into the air while concentrating the inorganic form left behind. Standard pitcher filters, water softeners, UV, chlorine — none of them are mercury treatments.
What I’d buy: Treatment type: an under-sink reverse osmosis unit, NSF listed — it’s the straightforward, proven answer for inorganic mercury in drinking and cooking water. Test first, retest after install.
Mercury doesn’t announce itself — no taste, no smell, no staining. If your well sits near industrial history, landfills, or heavy agriculture, a metals panel is cheap insurance. And if it’s there, RO takes it out.
Curious what’s in your tap? Start with What’s In Your Water?
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