Tannins in Well Water: Why Your Water Is Yellow (And How to Remove It)

Yellow or tea-colored water that stays yellow even after it sits in a glass usually means tannins: dissolved organic compounds from decaying leaves and vegetation that leach into shallow groundwater. Tannins are not a health hazard, but they stain laundry and fixtures, taste tangy, and will not respond to an iron filter. Here is how to confirm them, and what actually removes them.

A verified buyer wrote in September that after "installing an iron eater, softener, and filters, we still had stains in grout and toilets." He tested for tannins, put in a tannin filter, and wrote, "Water is beautifully clear finally."

Is it tannins or iron?

Fill a clear glass with your water and let it sit overnight. If the color stays, it is most likely tannins. If it settles to the bottom, it is most likely iron or manganese. The Water Systems Council says this test is not guaranteed and should be followed by a certified lab test. Wisconsin's natural resources department adds a second check you can do at the faucet: water that is already brown as it leaves the tap points to tannins, and water that comes out clear and changes color after sitting points to iron.

I tell people the same thing by color. If you had tannins, you would have a yellowish tinge to the water. If it's a reddish-orange tinge, that's red water iron. But yellow can be iron too, so the color alone does not settle it.

Iron can come with tannins, so test for both. The Water Systems Council notes that iron shows up as a false positive on a tannin test and has to be subtracted from the tannin result, which is one more reason to test for iron at the same time. If your glass settles orange, our iron filters page is the place to start.

Is it safe to drink water with tannins?

Yes. Tannins are not a health risk. The Water Systems Council calls them an aesthetic problem that presents no health risk. The EPA sets no limit for tannins. Its guidance on color says most people find color objectionable over 15 color units, and that is the real problem: yellow laundry, yellow stains on fixtures and dishes, and a tangy or tart aftertaste. Some wells also get a musty or earthy smell.

Tannins do cause trouble for other equipment. The Water Systems Council says the media in iron filters, water softeners and acid neutralizers can become coated by tannins and stop working properly, and recommends testing for tannins before installing any of them. A UV light needs them out first too: our UV system pages call for tannins under 0.1 ppm ahead of the UV chamber.

How to test for tannins

Only a lab can measure tannins. Our well water test does not include them. Our $99 tannin test measures one thing, tannins and lignins, at a certified lab. Our $199 well water test covers 53 values, including iron, hardness, pH and bacteria, but not tannins. Which one you need depends on what your glass did.

There is no tannin level where the water becomes unsafe, so the number does not work like a health limit. What matters is whether you can see the color, whether iron is adding to the reading, and whether you plan to put in a UV light.

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What removes tannins from well water

Tannins are fully dissolved organics, so sediment filters, iron filters, and standard carbon do very little. The standard whole-house fix is an anion exchange tannin filter: a resin tank that catches tannins and cleans itself with ordinary softener salt, the same way a water softener does.

That is what we sell. When a caller told me another company said only bleach would take his tannins out, I told him, "We have a filter that works like a softener that removes tannin. I've never heard of taking tannins out with the bleach."

Where the tannin filter goes

The tannin filter goes after the iron filter and the water softener. When I lay out a system for iron, hardness and tannins, the iron filter goes in first, then the softener takes out the hardness, and the tannin filter goes last. They are separate tanks. The reason is the resin: "you have to remove all the scale or dissolved hardness in the water before it goes into the tannin filter because the tannin resin, it's anion resin, and it'll try to remove the hardness and impair its ability to remove the tannins." The Water Systems Council says the same thing: most tannin systems include a water softener ahead of them.

1. Sediment filter. First, after the pressure tank.
2. Iron filter, if your test shows iron.
3. Water softener, if your water is hard.
4. Tannin filter. After the softener.
5. Acid neutralizer, if the tannin filter drops your pH.

A tannin filter can lower the pH of the treated water. One caller with neutral well water measured a drop of about a point after his tannin filter, and our tannin filter pages say to expect about a point. I told him, "You just put a neutralizer after the tannin filter, and it'll bring it back up to 7." Put it ahead of the tannin filter and "you would have to get it up to, like, 8, 8.5." If your well is acidic before any treatment, the neutralizer may belong further up the line; my treatment order guide covers that, and I set its place from your test.

Which tannin filter size you need

We sell two tannin filters. Which one fits depends on the size of your home and how heavy your tannins are. Both regenerate with ordinary softener salt, and the control valve regenerates by the gallons you use, so the upkeep is keeping salt in the salt tank.

On the phone I put it this way: "the larger unit is $2,895 for a heavy, heavy tannin load." What ships: the resin tank with its control valve and the salt tank, with the resin in separate boxes. The resin is loaded into the tank at install, and drain tubing is not included. We recommend installation by a licensed plumber, and I support your plumber by phone at 800-460-5810.

The Water Systems Council says a tannin filter should be cleaned now and then with a baking soda and saltwater solution, and that a "fishy" smell means the resin is fouled and due for that cleaning. A tannin filter can also change the chloride, sulfate and alkalinity of your water, so they are worth watching on your next test. When the resin wears out, replacement tannin resin is $895 per cubic foot, and the tank and valve stay. How long the resin lasts depends on how much tannin and how much water goes through it, so I do not promise a number of years.

Frequently asked questions