Tannins in Well Water: Why Your Water Looks Tea-Colored
Tannins in Well Water: Why Your Water Looks Tea-Colored
By the WellWater HQ team
Tannins are organic compounds released as leaves, roots, and other plant material decay in soil, and they turn well water yellow, amber, or tea-colored when they leach into groundwater. Tannins are almost always an aesthetic problem, not a health hazard, though their presence can signal a shallow well or a compromised seal letting more surface water reach the aquifer than it should.
Wells near wetlands, swamps, bogs, or areas with a thick layer of decaying leaf litter and peat are the most common source, since that’s where the organic breakdown that produces tannins happens fastest. A shallow well, or one with a weak surface seal, picks up more tannin-carrying surface water than a deep, well-sealed well drawing from a confined aquifer.
Are tannins in well water dangerous to drink?
No, tannins themselves aren’t a recognized health hazard, and there’s no EPA enforceable limit for them; they fall under the EPA’s non-enforceable secondary standards, which cover aesthetic issues like taste, odor, and color rather than health risks. The EPA’s secondary guideline for color sits at 15 color units, a threshold set for appearance, not safety.
That said, tannin-stained water is worth investigating rather than ignoring, since a shallow well or a failing surface seal that lets tannins in can just as easily let in other things the seal is supposed to block. If your well has never shown tannins before and suddenly does, treat it the same as any sudden water change: retest for bacteria and check the wellhead and casing.
How is tannin level actually measured?
Labs measure tannin-driven color on the platinum-cobalt (Pt-Co) true color scale, reported in color units, the same scale behind the EPA’s 15-unit secondary guideline. A faint yellow tint typically reads in the 5 to 25 color unit range, while dark, iced-tea-colored water can read well over 100 units.
Total organic carbon (TOC) is often tested alongside color, since tannins are one form of dissolved organic carbon; a lab report showing both numbers gives you a clearer picture than color alone of how much organic material is actually in the water.
What removes tannins from well water?
Anion exchange resin is the standard fix. Tannin molecules carry a negative charge in water above roughly pH 6, which lets a resin bed swap them out for chloride ions the same way a water softener swaps hardness minerals, and the resin regenerates with ordinary salt (Water Systems Council, Tannins & Well Water, 2026). Standard water softening resin, by contrast, isn’t tannin-specific and won’t reliably clear a tannin problem on its own.
If your well also carries iron or hardness, treat those first; iron and hardness minerals foul tannin resin faster and shorten its life between regenerations. Activated carbon can pull out some tannin-related taste and odor, but it’s a partial fix at best for actual color removal compared to a dedicated anion resin system.
How is a tannin removal system sized?
| Water color | Approximate resin dose | Result |
|---|---|---|
| Light yellow tint | About 1 lb resin per inch of tank diameter | Clears light tannin staining |
| Amber to tea-colored | Up to 2 lb resin per inch of tank diameter | Needed for heavier, dark tannin loads |
A system undersized for how dark your water actually runs will clear color for a while, then start slipping through tannin again between regenerations sooner than expected. Your lab’s true color number is what a water treatment professional uses to size the resin bed correctly the first time, rather than guessing from how the water looks in a glass.
What does tannin treatment cost?
A dedicated anion exchange tannin system runs $800 to $2,500 installed for most residential setups, depending on tank size and whether iron or hardness pretreatment is also needed ahead of it. Ongoing cost is mainly salt for regeneration, similar to running a water softener, plus periodic resin replacement every several years as it loses capacity.
For very high tannin loads, some setups add oxidation, typically chlorination, followed by filtration, though that’s a step up in complexity and cost from a standard resin system and usually only needed for the darkest water.
How is tannin-stained water tested and confirmed?
A certified lab test reporting true color in color units, ideally alongside TOC, confirms tannins rather than another cause of discolored water, like iron or manganese, which stain differently and need different treatment. Run the test whenever discoloration first appears, and again after installing treatment to confirm the resin bed is sized correctly.
Run your lab’s color and TOC numbers through the WellWater HQ test result checker to see whether a tannin-specific resin system or a broader filtration setup fits what your water actually needs. The WellWater HQ well water handbook covers how tannins compare to iron staining and other discoloration causes side by side.
FAQ
Are tannins in well water harmful to drink? No. Tannins aren’t a recognized health hazard and have no EPA enforceable limit, only a non-enforceable aesthetic guideline. They’re worth investigating because a shallow well or failing seal that lets tannins in can also let in other things, not because tannins themselves are dangerous.
What causes tea-colored well water? Decaying plant matter, leaves, roots, and peat, leaching tannins into groundwater. It’s most common in wells near wetlands, swamps, or bogs, or in shallow wells with more surface water influence.
Will a water softener remove tannins? Not reliably. Standard softening resin is built to swap calcium and magnesium for sodium, not tannins for chloride. Tannin removal needs a resin specifically selected for that exchange.
How much does a tannin filter system cost? A dedicated anion exchange tannin system runs $800 to $2,500 installed, depending on tank size and whether iron or hardness treatment is needed first. Ongoing cost is mainly regeneration salt.
How do I know if my discolored well water is tannins or iron? A certified lab test reporting true color and TOC alongside iron content tells them apart; both can turn water yellow or brown, but they stain differently and need different treatment systems.
Bottom line: tannins are almost always an aesthetic issue, not a health risk, and a properly sized anion exchange resin system clears them reliably. Get a true color and TOC test first so the system is sized to your water’s actual tannin load, not a guess.