Zinc
Zn·Affects liver
EPA secondary standard 5 mg/L (cosmetic, not enforceable). Zinc gives water a metallic, slightly astringent taste and a milky appearance at higher levels. The most common source is corrosion of old galvanized steel plumbing.
Zn
EPA limit
5 mg/L (SMCL)
Most at risk
Homes with aging galvanized plumbing, anyone with low-mineral feed water
Found in
City water · Well water
AquaOx filters
YesActivated carbon + KDF-55
What it does to you
Health effects
Zinc is an essential dietary mineral and is not a health concern at the concentrations found in drinking water. The EPA secondary standard of 5 mg/L is set for taste, not toxicity. At that level water becomes noticeably metallic and astringent, and may take on a milky appearance from precipitated zinc compounds.
Acute health effects from drinking water are essentially unheard of. The body absorbs zinc efficiently from food and regulates it well. The upper tolerable intake for adults is around 40 mg/day; reaching that from drinking water alone would require consuming 8 liters of water sitting at the SMCL.
The one indirect concern is that high zinc in tap water is usually a marker for galvanized-pipe corrosion, which also leaches cadmium and sometimes lead at the same time. So a metallic-tasting house with old plumbing should test for lead and cadmium alongside zinc.
Where it comes from
How it gets into your water
The dominant source of zinc in residential drinking water is corrosion of galvanized steel pipes. Galvanized pipe is steel coated in a layer of zinc; as the coating breaks down over decades, zinc dissolves into the water flowing through it. Homes built before the 1960s often still have galvanized supply lines somewhere in the system.
Other sources include the brass fittings and fixtures used throughout most plumbing systems, which contain a small percentage of zinc. Natural geological zinc occurs in some well water, especially in regions with mining history, but at much lower levels than corrosion-derived zinc.
Galvanized steel plumbing
Aging zinc coating dissolves into the water
Brass fittings
Small contribution from valves and faucets
Natural geology
Zinc-bearing minerals in some aquifers
Mining and smelting
Localized contamination near industrial sites
Find out for yourself
Is it in your water?
A metallic or astringent taste in cold water that is worst on the first draw of the morning is the classic galvanized-pipe-zinc signature. The first-draw pattern matters because zinc leaches faster when water sits stagnant in the pipes overnight. White or milky appearance at higher concentrations confirms it.
A standard plumbing-corrosion test panel from a certified lab gives you zinc, lead, copper, and cadmium together, which is the right combination to order if you suspect galvanized pipes. Running the cold tap for 30 seconds before drinking helps, but the long-term answer in an old house is usually to replace the supply lines or install whole-house filtration that handles the dissolved metals.
The fix
How AquaOx filters it
Zinc is captured by a combination of activated carbon adsorption and KDF-55 redox media, both of which are core stages in every AquaOx whole-house system. The KDF-55 in particular is highly effective on dissolved heavy metals, exchanging less-reactive ions for more-reactive ones and precipitating the targets out for the downstream sediment stage to catch.
For homes with aging galvanized plumbing, the AquaOx not only handles zinc but also captures the cadmium and lead that typically accompany it. That makes whole-house filtration a sensible alternative (or interim solution) to repiping an entire house, which can run into the tens of thousands of dollars.