Tannins in Water: How to Remove Tannins From Well Water (Tannin Filter Guide)
By SubcontractorHub Editorial Team·Published September 2026
Short version: tannins are dissolved organic matter from decaying vegetation, and they turn well water yellow to tea-colored. The tell is a glass of water that stays evenly tinted and never settles. The standard fix is a tannin filter: an anion exchange resin tank that regenerates with salt. Remove iron first, because iron fouls tannin resin, and deal with hardness in the same plan. Carbon only suits trace levels, and ozone or chlorine oxidation earns its cost when tannins arrive with iron and sulfur smell.
Tannin water looks alarming and is usually more of a nuisance than a hazard. It stains laundry and fixtures a pale yellow, can taste earthy or slightly bitter, and does not go away with a softener or a sediment filter. This guide covers how to confirm tannins, what the ppm number means, the treatment options side by side, and a worked sizing example. The last section is for the water treatment dealers who quote these systems.
1. What Tannins in Water Are
“Tannins” is the water treatment shorthand for natural organic matter, mostly humic and fulvic acids, that leaches out of decaying leaves, roots, peat and other vegetation. Rain and snowmelt carry it down through organic-rich soil into the aquifer. It is most common in shallow wells, wells near swamps, bogs, marshes or peat, and coastal lowlands with high water tables. Deep wells in rock are less likely to have it.
Labs usually report tannins in parts per million (ppm, the same as mg/L) as tannic acid equivalent. There is no EPA health limit for tannins. The nearest federal guideline is the EPA secondary standard for color: 15 color units, a non-enforceable aesthetic guideline. Levels often rise after heavy rain or spring melt and drop in dry months, so one test can understate the problem.
2. The Glass Test: Tannins or Iron?
Iron and tannins both give well water a yellow or brown cast, and they need different equipment. The quickest way to tell them apart is to fill a clear glass from a cold tap and leave it on a white surface for several hours to a day.
- Color settles to the bottom as orange or brown particles and the water above clears: that is oxidized iron.
- Color stays evenly spread through the glass with nothing settled: that is tannins, because the color is dissolved, not suspended.
- Some settles, but the water stays tinted: you probably have both, which is common and changes the order of treatment.
Another clue is water that is still yellow after a softener, since softeners remove some iron but no tannins. For every other cause of discolored water, including rusty pipes and water heater sediment, see why is my water brown. Always confirm with a lab or dealer test for tannins, iron, manganese, hardness and pH before choosing equipment.
3. What the ppm Number Means
These bands are practical rules of thumb used when quoting, not regulatory thresholds. Resin and equipment makers publish their own limits, and those govern.
Under about 0.5 ppm: faint tint, often only visible in a full tub. Carbon, a mixed-bed softener or a small tannin unit usually handles it. Enough to matter for UV.
About 0.5 to 3 ppm: clearly yellow in a glass and staining laundry. A dedicated tannin filter, or a mixed-bed unit at the low end with hardness present.
Over about 3 ppm: tea to dark tea color. A dedicated, generously sized tannin unit with frequent regeneration, or oxidation plus filtration when iron and hydrogen sulfide are also high.
4. Tannin Removal Options Compared
Installed costs are typical US ranges and vary with tank size, brand, plumbing and local labor.
How a tannin filter works
A tannin filter looks like a softener: a resin tank, a control valve and a brine tank. The difference is the resin. Tannins carry a negative charge, so they are captured by a strong-base anion resin that trades them for chloride. During regeneration, salt brine pushes the tannins off the resin and down the drain, and the brown rinse water is normal. Some dealers also schedule an occasional resin cleaner to strip organics the brine leaves behind.
Carbon works by adsorption and does not regenerate, which is why it runs out quickly on stronger tannin water. Oxidation with ozone or chlorine breaks the color down and is followed by a backwashing filter or carbon; see ozone water treatment for how that train is built. Reverse osmosis belongs at the kitchen tap after whole-house treatment, not as the tannin fix.
5. Treatment Order: Iron, Hardness, Then Tannins
Iron is the main reason tannin systems fail early. Iron coats anion resin and is hard to remove from it, so most resin makers want iron close to zero on the water entering a tannin unit. If the test shows more than a trace of iron or manganese, put an iron filter first. Tannins also bind iron into organic complexes that some iron filters struggle to catch, which is another reason to test both before quoting.
A typical well water train runs: sediment filter, iron filter, softener, tannin filter, then UV. Feeding the tannin unit softened water keeps hardness from depositing on it, and some installers plumb its brine draw from softened water for the same reason. On moderate tannins with hardness, a single mixed-bed tank can replace the softener and tannin pair. The water softener sizing calculator covers the hardness side, and the well water treatment system selector lays out the full sequence.
UV goes last for a reason. Tannins absorb ultraviolet light, lowering the water’s UV transmittance, and they stain the quartz sleeve. Many UV manufacturers list a maximum around 0.1 ppm tannins in their water quality specs. Size UV on the treated water with the UV water sterilizer sizing calculator.
6. Worked Example: Sizing a Tannin Filter
Tannin units are sized on two numbers: service flow, so water gets enough contact time at peak demand, and regeneration interval. Anion resin is usually run at a lower flow per cubic foot than softener resin. The figures below are illustrative; use the resin data sheet for real jobs.
Test: tannins 2.5 ppm, iron 1.2 ppm, hardness 12 gpg, pH 6.8. Four people, about 300 gallons a day, peak about 8 gpm.
Train: iron filter, then a softener sized for 12 gpg, then the tannin unit, then UV.
Resin volume: assume a rated service flow of 4 gpm per ft³. 8 gpm ÷ 4 = 2 ft³ of tannin resin, a common 12 x 52 in tank size.
Regeneration: assume the data sheet rates 2 ft³ at about 6,000 gallons per cycle at this tannin level. 6,000 ÷ 300 = 20 days, but set it to every 5 days, since organics held too long get harder to strip.
Salt: at about 8 lb per ft³, 16 lb per regeneration × 6 per month = roughly 96 lb a month for the tannin unit, on top of the softener.
The salt line is the one to show the homeowner up front. Tannin units use more salt than most people expect, and a customer who knows that in advance is far less likely to turn the regeneration down and foul the resin. If the peak flow were 12 gpm, the same math gives 3 ft³, a larger tank and a higher price. For a carbon polish stage after the resin, check contact time with the carbon filter sizing calculator.
For Water Treatment Dealers
Tannin calls are good calls. The homeowner has usually already bought a softener or a cartridge filter that did not fix the color, so the in-home water test is where you earn the job: run the glass test in front of them, test iron alongside tannins, and explain why the order of equipment matters. That explanation is what separates a dealer quote from a box-store unit.
The quoted system is usually a two- or three-tank train, which makes it a natural good-better-best proposal: mixed-bed only, iron filter plus tannin unit, or the full train with UV. The recurring revenue is the service plan. Tannin resin needs cleaning and eventual replacement, salt use is high, and seasonal swings mean settings need a check each spring. Bypass loops, drain runs and tank placement are plumbing work, so some dealers pair with a plumber on larger installs.
SubcontractorHub is software for water treatment dealers: proposals that carry the water test results, tiered system options, e-signature and recurring service scheduling in one place.
Frequently Asked Questions
Are tannins in water harmful?
Tannins are generally treated as an aesthetic problem rather than a health one. There is no EPA drinking water limit for tannins themselves; the closest federal guideline is the EPA secondary standard for color, 15 color units, which is non-enforceable and based on appearance. Two practical cautions apply. Tannins often show up in shallow wells that are also more exposed to surface water, so a well with tannins should be tested for coliform bacteria. And if tannin water is chlorinated, the organic matter can react to form disinfection byproducts, which is one reason tannins are usually removed before chlorine is added.
Will a water softener remove tannins?
A standard softener does not. Softener resin is a cation resin that swaps calcium and magnesium for sodium, and tannins are negatively charged organic molecules that pass through it. Tannins need an anion exchange resin. Some manufacturers sell a mixed-bed unit that puts softener resin and tannin resin in one tank and regenerates both with salt, which works well at low to moderate tannin levels when hardness is also a problem.
How do I test for tannins in my water?
Start with the glass test: fill a clear glass and let it sit for several hours to a day. If the water stays evenly yellow or tea-colored with nothing on the bottom, suspect tannins. If orange or brown particles settle out, the color is mostly iron. Confirm with a lab or a dealer test kit that reports tannins in parts per million as tannic acid, and test iron, manganese, hardness and pH at the same time, because those results decide the order of treatment.
Does a carbon filter remove tannins?
Activated carbon does adsorb tannins, but its capacity for them is limited and it can be used up quickly. Carbon makes sense for very low tannin levels, for a drinking water tap, or as a polishing stage after a tannin resin unit. At higher levels, a whole-house carbon tank alone tends to let color through within months, and replacing the media that often costs more than a tannin filter would.
Why do tannins in my well come and go?
Tannin levels in shallow wells often change with the seasons. Heavy rain, snowmelt and high water tables flush more dissolved organic matter from soil, leaves and peat into the aquifer, and dry periods can bring levels down. That is why a single low test in late summer can underestimate the problem, and why tannin systems are sized for the worst season the homeowner describes, not only the day of the test.
How long does tannin resin last?
Tannin resin wears out faster than softener resin because organic matter gradually fouls it. Service life is often quoted in the range of three to five years, and less on high-tannin water, water with iron getting through, or a system that regenerates too rarely. Regular regeneration, an occasional resin cleaner and good iron pre-treatment all extend it. Falling performance with a clean brine tank and correct settings usually means the resin is due.
Related Guides & Tools
- Why Is My Water Brown?
- Iron Filter for Well Water
- Ozone Water Treatment
- Well Water Treatment System Selector
- Water Softener Sizing Calculator
- Carbon Filter Sizing Calculator
- UV Water Sterilizer Sizing Calculator
- → SubcontractorHub for Plumbing
- → Water Treatment and Water Purification Contractor Software
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