The two forms of iron
Ferrous (clear-water) iron is dissolved and invisible until air hits it — you'll see rust settle out in a bucket after a few minutes.
Ferric (red-water) iron is already oxidized when it leaves the tap; the water comes out cloudy orange.
Iron bacteria form a slimy, reddish film in toilet tanks and clog well screens; they require shock chlorination in addition to filtration.