Tea-colored well water: tannins, how to tell them from iron, and what removes them

Short answer

Well water that is yellow or tea-colored at the tap, and is still that color after a glass has stood overnight, is most likely tannins: natural organic material picked up from peaty soil and decaying vegetation, per the Water Systems Council. Color that settles to the bottom of the glass is iron or manganese instead. EPA’s secondary standards list color at 15 color units, iron at 0.3 mg/L and manganese at 0.05 mg/L; tannins have no EPA standard at all. Confirm with a certified lab that reports tannin and iron together, because the Water Systems Council says iron reads as a false positive on a tannin test and has to be subtracted from the result. Sediment filters, greensand and softeners pass dissolved tannins through and can be coated by them. The treatment class is a tannin-selective anion exchange resin, usually with a water softener ahead of it; activated carbon with the right pore structure at lower levels; reverse osmosis or distillation at the tap for any level.

Do not buy an anion resin tank off a stain: the same yellow water has three different fixes, and an overnight glass plus a lab result for tannin and iron together is what tells them apart.

Does the color settle, or does it stay?

The glass check sorts tea-colored water into its likely cause before a lab report arrives, and the cause decides the treatment class. Tannins are dissolved, so they stay in solution; iron particles are solids, so they fall out.

Tannins, also written as fulvic or humic acid, are the byproduct of water passing through peat and rotting vegetation. The Water Systems Council says they are more common in surface water and shallow wells than in deep wells, and in marshy, low-lying or coastal areas.

What the glass shows after standing overnight	Likely cause	Confirm with
Faint yellow to tea color, the same intensity as when poured, nothing on the bottom	Tannins: the Water Systems Council says color that keeps its intensity is most likely tannins	A certified-lab tannin result with iron subtracted
Poured clear, then rust-colored or black particles settle to the bottom	Ferrous iron or manganese: Virginia Cooperative Extension says dissolved Fe2+ and Mn2+ appear clear at first and form particles on standing	A lab result for iron against 0.3 mg/L and manganese against 0.05 mg/L; see iron in well water
Brownish-black, rust, red or yellow when poured, particles settle	Ferric iron or manganic manganese: Virginia Tech says the oxidized forms are already suspended particles	The same lab panel; this is a filter problem, covered on the iron page
Yellow or brown, or no color at all, from a very shallow well	Organic iron: the Minnesota Department of Health says it is usually yellow or brown but may be colorless, and is more likely in shallow wells or wells affected by surface water	A lab result for both iron and tannin, since organic iron travels with them
Tangy or tart aftertaste, musty or earthy odor, yellow stains on laundry, fixtures or china	Also tannins: these are the other signs on the Water Systems Council sheet	The same tannin-plus-iron result

The council is explicit that the glass check is not guaranteed and should be followed by a certified lab test. Use it to decide which lab panel to order, not as the answer.

What does the lab have to separate?

The number that matters is tannin with iron taken out of it, and the lab can only do that if you order both. The Water Systems Council says iron creates a false positive for tannins and must be subtracted from the tannin result to give the true tannin concentration.

The council’s companion list for a tannin panel is alkalinity, chloride, hardness, iron, pH, sodium, sulfates and total dissolved solids. Hardness and pH pick the pretreatment; the rest are the values an anion resin can shift, so a baseline is worth having.

Line on the report	Reference figure	Who sets it	Why it is on this panel
Color	15 color units	EPA secondary standard	The nuisance threshold for visible color; tannins have no standard of their own
Iron	0.3 mg/L	EPA secondary standard	Subtracted from the tannin result; picks the iron treatment row if it is the real cause
Manganese	0.05 mg/L	EPA secondary standard	The other settling color; black to brown rather than yellow
pH	6.5 to 8.5	EPA secondary standard	Carbon adsorbs organics better at lower pH (WQA); greensand needs 6.8 or more (NDSU)
Total dissolved solids	500 mg/L	EPA secondary standard	Baseline before an anion resin changes chloride and sulfate

One stated gap: no regulator or extension source here names a specific “TOC test” or “tannin test” product for homeowners.

The Water Systems Council says a certified lab confirms tannins, and the Wisconsin DNR says private labs evaluate tannin, sulfur and iron problems. Ask for a tannin or total organic carbon line item by name, with iron on the same order.

Why does the filter you already have not fix it?

Because tannins are dissolved, not suspended. A sediment cartridge catches particles, and the whole-house sediment filter that clears ferric iron passes tea color straight through.

Iron equipment does worse than nothing. The Water Systems Council says tannins can coat the resins and media in iron filters, cation exchange softeners and neutralizing filters until they no longer work properly, and recommends testing for tannins before installing any of them.

The Minnesota Department of Health gives the mechanism: organic iron and tannins can slow or stop iron oxidation, so softeners, aeration systems and iron filters may not work well on that water.

Greensand shows the mismatch. NDSU Extension rates it to 10 mg/L of iron, wants pH of 6.8 or more, and backwashes it at about 8 gallons per minute per square foot of bed: every figure is about iron particles, none about dissolved organics. Virginia Tech’s softener ceiling of 5 mg/L combined iron and manganese says nothing about tannins either.

Certification does not help either. NSF’s summary of NSF/ANSI 42 lists chlorine, taste and odor, chloramine, particulate, iron, manganese, zinc and total dissolved solids as covered claims, and Wisconsin DHS’s November 2024 device table (P-03494) has no tannin row. A certified carbon filter carries no tannin claim.

Which treatment class fits?

Match the confirmed tannin level to a row. The Water Systems Council names three tannin technologies: anion exchange resin, ultrafiltration, and oxidation followed by filtration. Carbon and reverse osmosis come from the WQA and Minnesota sources.

Situation	Treatment class	Why, and the conditions
Lower tannin level, whole house	Granular activated carbon with a de-colorizing pore structure	WQA: tannins are high-molecular-weight organics that GAC can remove if the product has the right pore structure; wood-based GAC is the historic de-colorizing carbon. Adsorption improves at lower pH and slower flow
Moderate to high tannin level, whole house	Tannin-selective anion exchange resin, with a water softener ahead of it	WSC: an organic-scavenging anion resin trades negatively charged ions for tannins. The resin is sensitive to hardness, so most systems soften first, which extends resin life and increases tannin uptake
Drinking and cooking water only	Reverse osmosis or distillation at the tap	MDH: either removes any type of iron, including the organic iron bound to tannins. Heavy iron can quickly plug the unit, so whole-house treatment may be the better route
Iron confirmed as the real cause	The iron treatment table, not this page	Ferrous, ferric and bacterial iron each have their own row on the iron guide

An anion exchange resin is a bead that holds a positive charge and swaps the ion on it for a negatively charged tannin molecule.

As a manufacturer’s example, Purolite’s A860 data sheet lists a strong-base macroporous polyacrylic resin in chloride form, application “TOC/Tannin removal”, minimum total capacity 0.8 eq/L (17.5 Kgr/ft3), and a temperature limit of 80 °C (176 °F).

Its backwash expands the bed 50 to 70 percent for 10 to 15 minutes. Its WQA certification is to NSF/ANSI 61, which covers the material, not a tannin claim.

The resin row has upkeep. The Water Systems Council says the bed is regenerated occasionally with a baking soda and saltwater solution, that fouled resin gives the water a “fishy” odor when cleaning is due, and that the system can change alkalinity, chloride and sulfate levels.

Before you buy anything

Do not buy a resin tank, a carbon bed or an iron filter on the strength of tea color. The glass says whether the color settles; it does not say whether the tannin number is real or an iron false positive, whether hardness will foul the resin, or whether the pH suits carbon. A certified-lab panel for tannin, iron, hardness and pH is the purchase that decides the next one. The Wisconsin DNR’s rule is a test every year and after any change in taste, odor or appearance.

What should you do first?

Run the overnight glass check: color that stays is tannins, color that settles is iron or manganese, and a rotten egg smell is a separate guide.
Order a certified-lab panel with tannin (or total organic carbon) and iron on the same order, plus hardness and pH and the Water Systems Council’s companion lines.
Subtract iron from the tannin result, or ask the lab to; if iron is the real cause, switch to the iron guide.
Pick the row above: carbon for a lower level, softener-plus-anion resin for a higher one, RO or distillation if only the drinking tap matters.
For the resin row, size the softener stage with the water softener size calculator from the lab hardness figure; the hardness guide explains that number.

Frequently asked questions

How do I tell tannins from iron with a glass of water?

Fill a clear glass from the cold tap and leave it overnight. The Water Systems Council says color that settles to the bottom is most likely iron or manganese, and color that keeps its intensity is most likely tannins. Virginia Cooperative Extension adds that ferrous iron pours clear and forms particles on standing. The council calls the check not guaranteed: a certified lab test should follow.

Does a water softener remove tannins?

Not on its own. The Minnesota Department of Health says organic iron and tannins can slow iron oxidation, so water softeners, aeration systems and iron filters may not work well against them. The Water Systems Council says tannins can coat softener and iron-filter media and stop it working. A softener does belong in most tannin systems, but as pretreatment ahead of the anion exchange resin, not as the tannin remover.

Does activated carbon remove tannins from well water?

It can, with the right carbon. The Water Quality Association's GAC fact sheet says color bodies such as tannins are high-molecular-weight organics that granular activated carbon can remove if the product has the right pore structure; wood-based GAC has a long history of de-colorization use. Adsorption improves at lower pH and slower flow, so a carbon bed sized for chlorine taste is a different purchase.

Does reverse osmosis remove tannins?

The Minnesota Department of Health says distillation or reverse osmosis can remove any type of iron, including the organic iron that travels with tannins, and warns that a lot of iron can quickly plug the unit. An under-sink RO membrane covers the drinking tap only. Tea-colored laundry, fixtures and bath water still need whole-house treatment, which is where the anion resin or carbon bed goes.

Are tannins in well water a health risk?

The Water Systems Council lists tannins as an aesthetic problem: they can make water unappealing to drink and stain laundry, but the sheet says they present no health risk. EPA has no standard for tannins; its color standard of 15 color units is a non-enforceable nuisance guideline. The Wisconsin DNR says to test a private well yearly and after any change in taste, odor or appearance.