Tannin filters for well water

Best for

Wells with yellow, tan or tea-colored water and stains where a lab test shows tannins or high color and iron is low or already treated.

Wrong fit

Homes whose discoloration comes from iron or manganese, or whose color appears only after heavy rain. Those need an iron filter or a bacteria test and a well inspection first.

Tradeoff

It uses salt and water to regenerate, adds a brine tank, and the resin wears out over years, especially if iron or sediment reach it.

What tannins are and what they look like

Tannins are natural organic compounds that leach from decaying leaves, roots and peat, so they tend to turn up in shallow wells and in wet, wooded or peaty areas. In the water they show up as:

• Yellow, tan or weak-tea color, even after the water sits.
• Yellowish stains on fixtures and laundry.
• Sometimes an earthy or musty taste.

WQA lists tannins alongside metals as a cause of staining that affects fixtures throughout the house, which is why they are usually treated at the point of entry. EPA’s secondary standard for color is 15 color units. Like the other secondary standards, it is an aesthetic guideline, not an enforceable health limit. More on tannins in well water.

Tannins or iron? Test before you buy

Iron and tannins can both make water yellow or brown, and the treatments are different. Get a lab test that includes:

• Iron and manganese, to rule out or size an iron filter.
• Color, and tannins if the lab offers it. Tap Score lists tannins in its Extended Well Water Test, for example. Many state-certified labs can run color.
• Hardness and pH, because they affect which tannin unit fits.

If the color shows up mostly after heavy rain, also test for coliform bacteria. Penn State Extension notes bacteria levels in wells tend to peak after several weeks of wet weather, and surface water reaching a well can carry both organic color and bacteria. See how to test well water.

How a tannin filter works

A tannin filter is an ion exchange tank, similar in shape to a softener, filled with anion exchange resin. Tannins carry a negative charge in water, so they attach to the resin and are held there. WQA lists anion exchange first among the treatments for stain-causing contaminants, along with activated carbon and filtration.

When the resin fills up, the control valve regenerates it with salt brine and rinses the tannins to a drain. The Minnesota Department of Health (MDH) notes two cautions for anion exchange: it can change how corrosive your water is, and if it isn’t maintained, the captured contaminant can be released back into the water.

Combination units. Some systems mix tannin resin and softener resin in one tank so a single unit removes both tannins and hardness. SpringWell’s STR system works this way: it pairs a sediment pre-filter with a single tank that removes tannins and softens, regenerated with salt from a brine tank.

Other options for tannins

Anion exchange is the usual whole-house answer, but WQA also lists activated carbon and filtration for stain-causing contaminants. How they compare:

Because tannins stain throughout the house, WQA says they’re typically treated for the whole house rather than at one faucet. A drinking-water-only filter makes sense only if the color is faint and nothing is staining.

Watch the treated water. As resin nears exhaustion, color creeps back. A faint yellow tint in a white bucket or toilet bowl can be the first sign. If color returns soon after regeneration, check the salt level and settings before assuming the resin is spent.

What has to come first

A tannin unit is a resin bed, so it shares a softener’s weaknesses:

• Iron and manganese. Penn State says oxidized iron clogs softener resin. On a combination tannin and softener unit, keep iron and manganese out with an iron filter ahead of it, and ask the manufacturer for its iron limit in writing.
• Sediment. A pre-filter keeps grit off the resin. SpringWell includes one with its tannin system.
• pH. Check the unit’s range. SpringWell lists pH 6.5 to 10 for its STR models.

Typical order:

1. Sediment filter.
2. pH neutralizer, if pH is low.
3. Iron, manganese and sulfur filter. See whole house well water filters.
4. Tannin filter or combination tannin and softener.
5. UV, last. Color reduces how much UV light reaches microbes. SpringWell’s UV spec, for example, calls for tannins below 0.1 mg/L (ppm). See UV systems.

Sizing and install needs

SpringWell’s published specs give a sense of a typical combination unit:

Note the 60 psi top limit. If your pressure switch is set higher, you may need a pressure-reducing valve.

You’ll also need:

• A drain for regeneration rinse water. SpringWell’s guide lists backwash rates of 2.4 GPM (STR-1) and 3 GPM (STR-4).
• Power for the control head.
• Floor space for the resin tank and brine tank side by side.
• A bypass valve for service and for shock chlorination.

Maintenance

• Salt. Keep the brine tank stocked. Penn State notes a softener regeneration uses about 50 gallons of water, and tannin units use a similar brine-and-rinse process.
• Pre-filter cartridges. Change them when flow drops.
• Resin replacement. MDH’s cost table lists anion exchange media maintenance every 8 to 10 years. Expect shorter life if iron or sediment reach the resin.
• Resin cleaning. Penn State notes bacteria and fungi can form mats in ion exchange resin, and periodic cleaning can help. Follow the manufacturer’s instructions.
• Retest. Check color, hardness and iron in the treated water after install, then yearly.

The brine can be made with sodium chloride or potassium chloride. MDH notes both are safe to handle and easy to buy. Because anion exchange can change how corrosive the water is, test first-draw copper and lead after installation if your home has copper plumbing.

MDH also points out that salt use can harm the environment. Set regeneration to match your actual tannin and hardness levels rather than the factory default.

Who should skip it

• Iron is the real cause. Treat with an iron filter and retest the color afterward.
• Color only after storms. Test for bacteria and have the well cap, casing and grading checked.
• Very light, occasional color that doesn’t stain or bother you.
• High iron with no plan to pretreat. The resin will foul.
• Homes that also need softening but want to avoid two tanks. A combination unit may suit you better than separate tannin and softener tanks. See water softeners for well water.

When to call a pro

Bring a lab report to a water treatment professional if tannins, iron and hardness are all present, or if a tannin unit stops clearing the color within a year or two. To see which steps your numbers call for, enter them at /test-results/.