FAUCET FACTS
Black grit on plumbing fixtures isn’t necessarily a health concern
Q Every few months, when I rub a cloth under my kitchen faucet, the cloth comes away with little black pieces. It happens with my shower head, too. Is this mould? Should I be concerned?
A
The black deposits on your kitchen faucet might be mould, said Kathryn O’brien, a communications specialist for the Arlington County Department of Environmental Services who looked at the picture you sent. “The faucet head in the picture has several tiny sprayers,” she noted in an email. “These types of kitchen faucets are more susceptible to mould because the surface can be damp, and it is likely exposed to food, which can contribute to mould growth. Cleaning it with bleach or another household cleaner will remove the mould.”
However, the grit you’re seeing is probably something else. Assuming that you’re seeing the black bits only when you occasionally wipe the faucet spout and shower head, the deposits are probably oxidized manganese, a mineral that’s often found in trace amounts along with iron in drinking water. Both can be picked up as the water travels through soil and rock, although iron can also come from corroding pipes made of galvanized steel. Where the water hits air — on the aerator of a kitchen faucet or on a shower head, for example — the minerals combine with oxygen.
Oxidized iron forms the yellowish or reddish deposits we know as rust; oxidized manganese is brown or black. The particles can also settle out when a glass of water is poured. Sometimes, in addition to the gritty oxidation, there is also a black slime, which is caused by bacteria that feed on oxidized iron and manganese.
A little iron or manganese in water isn’t a problem, and even a little of the slime isn’t a health hazard. (But if that grosses you out, O’brien suggests cleaning it with a mild bleach solution.) Iron and manganese are actually essential for good health — in trace amounts.
Too much can be a health hazard, and it can make the water taste bitter and stain sinks, toilets and laundry. The U.S. Environmental Protection Agency has no mandatory limit for either iron or manganese, but it does recommend that iron be below 0.3 milligrams per litre and manganese be below 0.05 mg/l to guard against bad taste and staining.
If you have a private well, however, the manganese level could be higher. High manganese is typically more likely in well water than in surface water. Owners of private wells are responsible for testing their own water and for treating it if necessary.