Tannins in well water

Best for

Homes with yellow or brown water that stays colored after 24 hours, a lab result showing tannins or color, and pH of 6.5 or higher.

Wrong fit

If the color settles to the bottom of a glass, it is iron, not tannins. Wells with a positive coliform test should fix bacteria first.

Tradeoff

Tannin resin regenerates with salt like a softener, and wells with tannins plus iron often need a separate iron step, which tannins can make harder.

What tannins look like

Tannins, sometimes called humic acid, are natural organic compounds released as plants decay. North Dakota State University Extension says they are common where water passes through coal veins, peaty soils and decaying vegetation. Shallow wells and wells influenced by surface water are the usual suspects.

The signs:

• Water that is pale yellow to tea-brown, even right after filtering or softening.
• Color that does not clear up after the water stands for 24 hours, the test NDSU uses to separate tannins from other causes.
• A tint you can see in a white tub, sink or toilet bowl.

Tannins or iron? Do the glass test

Fill a clear glass and let it sit overnight.

• Color settles to the bottom as orange or brown particles, and the water above clears: that is iron. See iron in well water.
• Color stays evenly spread through the glass: that is tannins or another dissolved organic.
• Some of both: many wells have tannins and iron together. The Minnesota Department of Health describes “organic iron” as yellow or brown, more likely in very shallow wells or wells affected by surface water.

The Minnesota Department of Health describes three kinds of iron, which helps you read what you see at the tap:

The glass test points you in the right direction, but treatment should be sized on a lab result.

Is it a health risk?

Tannins are not known to be a health risk. The EPA lists color as a secondary, cosmetic standard with a guideline of 15 color units, alongside other aesthetic issues like iron and manganese. Private wells are not regulated, so this is a guide, not a requirement.

The indirect concern is that tannins often signal shallow or surface-influenced water. Penn State Extension notes that coliform bacteria are much more common in springs and shallow wells than in deeper wells. A well with tannins deserves a coliform test.

How to test

Ask a state-certified lab for:

• Tannins and color, in color units
• Iron and manganese, since they often travel with tannins and change the treatment plan
• Hardness, because tannin systems often soften at the same time
• pH
• Copper, if you are considering a packaged tannin system; SpringWell’s listed conditions cap copper at 1.30 mg/L
• Total coliform bacteria and nitrate

The guide to testing your well covers sampling, and the test results tool can build a plan from your numbers.

What level needs treatment

There is no health-based limit for tannins, so the decision is about how the water looks and what other equipment you need to protect.

Treatment options

NDSU lists two ways to remove tannins: chlorination with a detention tank, or a special anion exchange unit.

For most tannin wells that also have hard water, a single tank that combines tannin resin and softening is the simplest choice. SpringWell’s tannin filter and softener is one option: SpringWell lists the STR-1 for 1 to 3 bathrooms (30,000 grains, 12 GPM) and the STR-4 for 4 to 6 bathrooms (45,000 grains, 15 GPM), both rated for pH 6.5 to 10 and an operating pressure of 25 to 60 psi. The tannin filter guide compares dedicated and combined units.

Tannins with iron or other problems. The same SpringWell page lists conditions for the water its systems treat: no hydrogen sulfide, no oils, and copper no higher than 1.30 mg/L. It also warns that iron or manganese will oxidize the media, and recommends pretreatment if any of these are present. That matches Minnesota’s caution that organic matter makes iron harder to treat. Minnesota adds that distillation or reverse osmosis can remove any type of iron at one tap, but a lot of iron quickly plugs those units, so a whole-house approach may be better.

Carbon filters for light color. NDSU Extension says activated carbon removes organics that affect taste, odor and color, and that if those are your only concerns, pour-through and faucet-mounted units will probably do the job, though they need more frequent filter changes. NDSU also cautions that a carbon filter loaded with organic material, or left unused for more than five days, can become a food source for bacteria, and recommends a sediment filter ahead of any carbon unit. For high-volume carbon filters, its rule of thumb is a change every three to six months, or sooner if flow drops or the problem returns.

Order of treatment

1. Sediment filter, if needed.
2. pH correction, if pH is below 6.5.
3. Iron, manganese or sulfur removal, if those are high. Organic matter can interfere, so ask the installer how the iron step will handle tannins.
4. Tannin resin, alone or combined with softening.
5. UV, last. Tannins, hardness and iron must all be low for UV to work.

Maintenance

• Keep the brine tank stocked; tannin resin regenerates with salt.
• Change any carbon filter on schedule, or sooner if color or taste returns.
• If color comes back, have the system serviced and retest the raw water, since the tannin level may have changed.
• Test treated water after installation to confirm the color and any iron are gone.

When to call a pro

Call a water treatment professional if tannins come with significant iron, if color returns quickly after treatment, or if you need UV for bacteria. A licensed well contractor can check whether surface water is getting into a shallow well. Your state health department can help with coliform results.