Tannins give well water a yellow, brown, or tea-like color and an earthy, musty taste. They stain laundry and fixtures. Anion exchange resin removes them effectively.
Tannins are naturally occurring organic compounds produced by the decomposition of leaves, bark, and other vegetation. In areas with peaty soil, high organic matter, or shallow aquifers, tannins leach into groundwater and create the characteristic yellow to brown 'tea-water' appearance. Tannins are not a health hazard, but they cause cosmetic problems — stained laundry, yellow sinks and toilets, and an unpleasant earthy or musty taste.
Standard carbon filters reduce tannins to some degree but are not effective against high concentrations. Anion exchange resin — the same technology used in water softeners but with a different resin type — is the most effective method for tannin removal.