Tannins are dissolved organic compounds leached from decaying vegetation, peat and leaf litter, and they arrive in a well as a yellow to tea brown tint that survives standing, settling and ordinary filtration entirely. They are not a health hazard at the levels usually found, and they stain laundry and fixtures and taste faintly earthy, which is complaint enough.
Confirming it is tannins
Colored water has several causes needing different treatment, so test before buying. Fill a clear glass and let it stand: water clearing from the bottom up carried suspended particles, water clearing from the top down carried gas, and water staying uniformly colored for hours carries something dissolved. That leaves tannins or dissolved iron. Iron reads more orange and leaves a rusty deposit; tannins read yellow to brown and stain fabric without leaving a deposit. A laboratory test settles it.
Anion exchange, the main treatment
A tannin removal resin is an anion exchange bed that binds the negatively charged organic molecules and regenerates with salt much as a softener does. It handles a real load well and is the standard answer. It has two requirements people miss: it must be protected from iron, which fouls it quickly, and it normally sits after a softener rather than before, so the softener deals with hardness and the tannin resin is not asked to do both jobs at once.
The alternatives and their ceilings
Activated carbon removes some tannins and is cheap, but its capacity is small relative to a genuine tannin load and beds exhaust quickly on truly colored water, so it suits light discoloration only. Oxidation with chlorine followed by filtration breaks the molecules down and works, but needs contact time and a carbon stage afterwards to remove the chlorine. Reverse osmosis removes tannins thoroughly at a single tap, which does nothing about the stained laundry that usually prompts the enquiry.
Design the whole train
Wells with organic color rarely carry only tannins. Iron, low pH and sometimes bacteria come with them, and each affects both the media choice and the order of stages. The EPA notes private wells are not federally regulated under the Safe Drinking Water Act, so the analysis is the owner's to commission. The usual sequence is sediment, then pH correction if needed, then iron, then softening, then tannin resin. Our well filtration guide covers the ordering in detail.
Questions people ask about tannins in well water
How do I tell tannins from iron?
Let a glass stand. Tannins stay uniformly yellow to brown and stain fabric without a deposit. Iron reads orange and leaves rust.
Are tannins harmful?
Not at the levels usually found in a well. The complaint is staining, color and a faintly earthy taste rather than health.
What removes them properly?
A tannin removal anion exchange resin regenerated with salt. Oxidation followed by carbon also works, as does reverse osmosis at one tap.
Where does tannin resin sit in the train?
After sediment, pH correction and iron removal, and normally after the softener so it is not also handling hardness.