Iron in well water: the orange stain on everything, and the number that decides the fix

The threshold

The federal secondary standard for iron in drinking water is 0.3 milligrams per litre. It is not a health limit, it is the concentration above which water stains and tastes metallic. Published United States Geological Survey work on Duval County found iron above that level in water from the shallow zones at seven of thirteen aquifer test sites, which is why the problem is so familiar on water-table wells here and less so on deep Floridan wells.

Two kinds of iron

Dissolved iron comes out of the tap clear and turns orange as it meets air; that is the water that stains a white sink over a week. Particulate iron arrives already orange and settles in a glass. Some wells also carry iron bacteria, which leave a slimy orange film in toilet tanks and clog screens. Each responds to different treatment, and a sample under a microscope or a simple settling test tells them apart.

Filter, softener or both

Small amounts of dissolved iron, below a milligram or two per litre, can be handled by a water softener, which exchanges iron the way it exchanges calcium. Above that, or where the iron is particulate or bacterial, a softener fouls quickly and an iron filter is the right tool: oxidising media that converts dissolved iron to solid and traps it, backwashed on a schedule. Where hardness is also high, the softener goes after the iron filter, never before.

Irrigation wells stain too

Iron sprayed onto a pale driveway, a white fence or the side of a house leaves orange streaks within a season. Where a test on an irrigation well shows iron, an iron stage on the irrigation line, or drilling to a deeper zone, is cheaper decided before the house is streaked than after.