However, the grit you see is likely something different. For example, suppose you only see the black spots if you occasionally wipe the faucet spout and shower head. The deposits are likely to be oxidized manganese, a mineral that is often found in traces with iron in drinking water. Both can be picked up as the water moves through soil and rocks. However, iron can also come from corrosive galvanized steel pipes. Where the water meets the air – for example the aerator on a kitchen faucet or a shower head – the minerals combine with oxygen. Oxidized iron forms the yellowish or reddish deposit 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 coarse-grained oxidation, there is also a black slime caused by bacteria that feed on oxidized iron and manganese.
A little iron or manganese in the water isn’t a problem, and even a little slime isn’t a health risk. (But if that bothers you, O’Brien suggests cleaning it with a mild bleach solution.) Iron and manganese are essential to good health – in traces. Too much can be harmful to your health and make the water taste bitter and dirty sinks, toilets and laundry. The Environmental Protection Agency has no binding limit for either iron or manganese, but recommends that iron be below 0.3 milligrams per liter and manganese below 0.05 mg / l to avoid bad taste and staining.
Arlington water comes from the Washington Aqueduct through the Dalecarlia water treatment plant. The Washington Aqueduct laboratory tests more than 65,000 water samples each year and reports the results on its website. The 2018 report shows the monthly tests for manganese ranging from 0.5ppm to 1.4 ppb averaging 0.77 ppb, which is 0.00077 mg / L – almost two orders of magnitude below the EPA recommended guideline of 0.05 mg / l.
However, if you have a private well the manganese levels could be higher. High levels of manganese are typically more likely in well water than in surface water. Owners of private wells are responsible for testing their own water and treating it if necessary. The Virginia Cooperative Extension has a publication titled “Virginia Household Water Quality Program: Iron and Manganese in Household Water,” which explains the problems and ways to treat the water to remove excess iron or manganese. This is done by adding phosphate to keep the minerals suspended in the water or by installing an ion exchange water softener.
The first step, however, would be to have your water tested if it came from a well. The Virginia Cooperative Extension sponsors the Virginia Household Water Quality Program (wellwater.bse.vt.edu), which operates clinics in most Virginia counties where well owners can have their water tested by the Virginia Polytechnic Institute and Virginia State University for results and learn how to interpret them in follow-up meetings. These tests include iron and manganese, as well as nitrate, lead, arsenic, fluoride, sulfate, pH, total dissolved solids, hardness, sodium, copper, total coliforms, and E. coli bacteria.
Well water in some parts of Virginia is high in manganese and iron, but the staining that usually causes well owners to have their water tested was apparently not a problem in Arlington County. “I don’t remember testing a well in Arlington for manganese,” said a Burke representative, Va., Water Testing Laboratory Office (800-200-5323; wtlmd.com) with three testing laboratories in Maryland and one in Virginia serving more than 1,000 water systems.