Water softeners for tannins

Best for

Wells with yellow to brown water that stays colored after standing for a day, pH of 6.5 or higher, and hardness you also want removed.

Wrong fit

Water whose color settles out or comes from iron alone, water below about pH 6, or wells with significant iron or hydrogen sulfide that has not been treated first.

Tradeoff

A tannin unit avoids adding chlorine but uses salt and water like a softener and adds chloride. Chlorination also deals with iron, sulfur and bacteria but needs a holding tank, a carbon filter and ongoing chemical supply.

What tannins are

Tannins are natural organic compounds from decaying plant matter. WQA describes them as part of the decay-resistant material formed as vegetation breaks down, found almost anywhere large amounts of vegetation have decayed, and able to give water a faint yellow to brown color. NDSU Extension says they are common where water passes through coal veins, peaty soils and decaying vegetation. Related humic substances can tint water yellowish-brown to brownish-black and, per WQA, can be detected at concentrations as low as 0.1 mg/L (ppm).

In practice, tannin water is often described as tea-colored; SpringWell uses that term for it.

Tannins or iron? Test before you buy

Both tannins and iron can turn well water yellow or brown, and they need different treatment.

The glass test. Fill a clear glass with cold water from a tap that does not go through any treatment, and let it stand for 24 hours. NDSU Extension says yellow to dark brown color that does not clear after standing 24 hours indicates tannins. NDSU also notes the color can remain even after softening or filtering, which is often how people discover they have tannins: they install a softener and the color stays.

A lab test. NDSU’s advice is to have your water tested and base treatment on the results. Ask for:

• Tannins
• Color, in color units
• Iron and manganese
• Hardness
• pH
• Hydrogen sulfide, if you notice a sulfur smell
• Coliform bacteria, especially for shallow wells

Both at once. The Minnesota Department of Health says organic iron and tannins present water treatment challenges. Organic iron is usually yellow or brown but may be colorless, is more likely in very shallow wells or wells affected by surface water, and, like tannins, can slow or prevent the iron oxidation that iron filters rely on.

Why a standard softener doesn’t work

A water softener uses cation exchange resin, which swaps positively charged ions such as calcium and magnesium for sodium. WQA’s glossary says tannin molecules tend to form anions (negatively charged ions) in water above about pH 6 and can then be treated with anion exchange resin. Cation resin is the wrong charge for the job. That is why color persists after softening.

WQA’s ion exchange fact sheet describes the anion resin used for this: strong base anion resin, which exchanges negative ions for chloride and, like softener resin, is regenerated with salt.

Treatment options

WQA lists four general ways to remove color bodies such as tannins: oxidation, coagulation and filtration, adsorption, and ion exchange. For a home well, the practical choices are these.

NDSU Extension’s recommendation is chlorination with a detention tank or a special anion exchange unit. WQA’s design course adds a warning for the chlorine route: always follow chlorine feed with an activated carbon filter, both for taste and odor and because chlorine reacting with natural organics in the water can form disinfection byproducts.

For water below about pH 5, WQA says tannins are better treated with activated carbon than with anion exchange.

Combination tannin and softener units

If your tannin well is also hard, a combination unit handles both in one tank with one brine tank. SpringWell’s Tannin Removal System is one example. Its published specifications:

A few points from the product page and manual are worth knowing before you buy:

• No published tannin limit. The product page does not state the maximum tannin level the unit handles. If your test shows heavy color, ask SpringWell for a limit in writing.
• No iron claim. The page does not claim iron removal or list an iron limit. SpringWell’s general warranty terms for private wells say iron or manganese will oxidize the media and recommend pretreatment if iron, manganese, hydrogen sulfide, oils or high copper are present.
• Small spec differences. The installation manual lists 25 to 80 psi for the STR-1 and pH 6 to 10 for the STR-4, slightly different from the product page. The page’s size guide also lists 9 and 12 GPM tiers that do not match the 12 and 15 GPM spec table. Ask which figures apply to the unit you would receive.
• Pre-filter included. The manual shows a sediment pre-filter in the system contents, installed ahead of the tank.
• Install needs. A drain for the 50-foot drain line, an outlet not controlled by a switch, room for the tank and brine tank, and a bypass valve.

Setting a tannin unit

Settings follow the same logic as a softener, with a tannin allowance. SpringWell’s STR manual says to enter a water hardness value equal to your tested hardness plus one for each level of tannins. The manual does not state the tannin unit, so confirm with the maker how to read your lab result. Its other settings:

• Regeneration at 2:00 am by default, staggered by 2 hours from any other treatment unit with its own control head
• Day override 14 days, reserve 10%
• Backwash 10 minutes, brine draw 60 minutes, rapid rinse 10 minutes
• Resin capacity 30 (STR-1) or 45 (STR-4), brine refill 12 minutes (STR-1) or 16 minutes (STR-4)
• Initial brine tank fill of 4 to 5 bags of salt pellets, then a forced first regeneration of about 90 minutes with no water

For how the hardness setting drives regeneration, see water softener settings, and for sizing by grains, see how to size a water softener.

If you also have iron or sulfur

Treat them in the right order. If your test shows iron above what a tannin unit’s maker will accept, or a sulfur smell, an iron filter usually goes first. But because organic iron and tannins can slow iron oxidation, an air-injection iron filter may not perform to its rating on tannin water. Discuss the full test with the maker before buying either unit, and consider chlorination with a holding tank and carbon if iron, tannins and bacteria all show up together. See iron and water softeners and iron filter vs water softener for the iron side.