Key Takeaways
- Tannins are organic molecules that are harmless to your body but can cause inconvenient staining around the home.
- Due to treatment of the public water supply, tannins are more likely to be found in well water than in municipal water.
- Several filtration methods, including reverse osmosis, anion exchange, and activated carbon, can effectively filter tannins from your water.
- To ensure the quality and safety of your drinking water, consider using Tap Score’s water testing kits.
How to Remove Tannins From Water
Life in the modern world has its advantages, including multiple advanced water filtration technologies.
Finding the right filtration method to remove tannins from your water involves testing your water to see what else is present. That way you can tackle multiple impurities with as few filtration systems as possible.
Reverse osmosis (RO)
RO systems force water through a semipermeable membrane that blocks large molecules like tannins while allowing water molecules to pass. Tannins are washed away with the RO’s wastewater stream.
RO is highly effective, removing up to 99% of tannins and other contaminants (e.g., salts, minerals, metals).
In household application, RO is most common in under-sink and countertop systems used specifically for drinking water. It’s often paired with pre-filters, such as activated carbon, to protect the membrane.
Reverse osmosis is popular due to its comprehensive contaminant removal and ability to produce high-quality drinking water. However, it doesn’t treat the entire home’s water supply, and it’s known to waste almost as much water as it produces, though advances in the technology have cut down on such waste.
Check out our review of the best whole-house reverse osmosis systems for more information.
Anion exchange
Anion exchange systems use resin beads charged with negatively charged ions (chloride from sodium chloride softener salt) to exchange with negatively charged tannin molecules, removing them from water (like a water softener, but for tannins instead of calcium and magnesium).
The resin beads are very porous and trap the tannin molecules. The filter system components are the same as a water softener. Only the resin is different. The resin is periodically cleaned (regenerated) with water softener salt.
Anion exchange is highly effective for tannin removal, especially in soft water, in a wide range of tannin concentrations and at large volumes of water.
You can apply anion exchange in whole-house or point-of-entry systems, often combined with water softeners. It does require periodic resin regeneration with a salt solution.
The only downside to anion exchange for tannin removal is that it’s less effective in hard water unless combined with softening. This requires a higher initial cost. But if you have hard water, there are plenty of reasons to tackle that as well as your tannins.
Activated carbon filters
Activated carbon filters adsorb organic compounds, including tannins, onto their porous surface. Granular activated carbon (GAC) or carbon block filters are commonly used. They’re effective for most tannin levels.
In households, activated carbon is common in under-sink or countertop filters (e.g., pitcher filters or faucet-mounted systems). These systems require regular filter replacement to maintain efficacy. A whole-house activated carbon filtration system can be used if tannin-free water is desired at every tap and toilet as well as the washing machine.
What’s nice about activated carbon is that it’s simple to install and use. It improves the taste and color of the water without producing harmful by-products.
However, activated carbon filters can clog or saturate quickly in homes with high tannin levels, and replacement costs can add up. In fact, the filter cartridges may need to be replaced as often as every six months. Keep in mind, though, that sediment and activated carbon filters should be replaced every six to nine months anyway, so this isn’t that big of a deal in the larger context of filter replacement.
Chlorination
For municipal water supplies, chlorination is often used to combat tannins. Chlorination involves adding chlorine to water to oxidize (break down) organic compounds, including tannins.
Chlorine breaks down tannins into smaller molecules that are more easily removed at the water treatment plant. Chlorination also disinfects the water, which is required by federal water regulations.
Chlorination is moderately effective for low tannin concentrations. Treating high tannin levels may require excessive chlorine, leading to by-products like trihalomethanes (THMs), which pose health risks. THMs are classified as carcinogenic “disinfection by-products.” The water treatment plant will use activated carbon filtration to remove THM’s from the chlorinated water.
Chlorination is typically used in municipal water treatment systems rather than household systems due to the need for precise dosing and by-product management. Some private wells with microbial contamination can have chlorine injection systems.
Ultrafiltration (UF) membranes
Ultrafiltration membranes use hydrostatic energy to force water through the filters. As a result, heavy molecular particles are trapped in the system while low-molecular-weight solute passes through the filter.
A semipermeable membrane captures many types of suspended contaminants in water, like natural organic material, bacteria and viruses, and other dissolved solids.
Most homeowners are not going to be able to select an industrial-grade UF membrane for their consumer-level RO system. While UF membranes are used in industrial treatment, you rarely see them associated with home use.
What Are Tannins?
Tannins are naturally occurring organic compounds known as “polyphenols” found in plants, bark, leaves, and fruits. In drinking water, tannins typically originate from decaying vegetation, including tree leaves, bark, and leafy vegetation, and are common in surface water sources like rivers, lakes, or wells near forested areas.
You may also find tannins in well water located near saltwater wetlands and forests that border estuaries and bays.
Tannins usually impart a yellow to brown color to water, depending on the type of tannin and the concentration in the water. They can cause a bitter or astringent taste. While tannins are not inherently harmful to human health, they can affect water aesthetics and quality, making treatment desirable for household use.
How Do Tannins Enter Water?
Tannins are generally more common in marshy, low-lying areas along the coast or near a body of water. When leaves, tree bark, and other types of vegetation decay, highly soluble tannin molecules are released into the soil and slowly find their way into the aquifer.
Sometimes, surface water, or local runoff, passes through the decayed leaves and tannin-rich soil and absorbs all the tannins before seeping into your well through cracked well walls.
Impact of Tannins on Drinking Water
Water extremely contaminated by tannins will appear yellow or brown, like tea or apple juice, depending on the concentration of contamination.
Did you know that the Blackwater River of Florida is black because of the presence of tannins? Well, now you do.
In addition to a darker appearance, tannins also affect taste and odor. The astringent in tannins adds a bitter taste and a musty, plant-like smell to drinking water.
Despite the physical effects, which may be alarming to the observer, tannin water is not toxic. Tannins are organic plant molecules that are harmless to humans. Many beverages and foods that we consume daily contain tannins, including coffee, leafy vegetables, and legumes.
What is problematic is the strong staining ability of tannins. Tannins can bind with metals like iron, forming complexes that cause staining on fixtures or laundry.
How to Test for Tannins in Well Water
It’s not a good idea to rely on appearance alone to diagnose a tannin problem. And there are no DIY testing kits that will test for tannins. You can buy a tannin test on the internet for about $300, but it doesn’t test for anything else.
That’s a lot of money to spend on something you’ll use once.
I’ve got a better idea.
Send a sample to a lab.
It’s often hard to distinguish tannins from ferrous and ferric oxide at home.
The best way to check for tannins in your water is to send a sample or send your tap water to an accredited laboratory. Laboratories use special methods to accurately determine the concentration of each type of contaminant in your water.
The results will help you get a good idea of what is lurking in your water.
You can either test only for tannins only or go for a package that covers ferrous, ferric oxide, manganese, total dissolved solids, volatile organic compounds, sulfur, and more to get a wholistic overview.
Considerations for Household Use
Tannin levels: It is possible to have a laboratory test the water to determine tannin concentration (typically measured in mg/L as tannic acid) to select the appropriate method. Low levels (<2 mg/L) may be managed with activated carbon, while higher levels may require anion exchange or RO.
Water chemistry: Hard water or high iron content can interfere with anion exchange tannin filters. Pre-treatment may be necessary.
Cost and maintenance: Activated carbon is the most affordable but may require relatively frequent filter changes. The truth is, activated carbon filters should be changed every 6–9 months anyway, so this is not unique to tannin filtration. RO and anion exchange systems have higher up-front costs. An anion exchange tannin filter system works much like a traditional water softener. You’ll have to periodically add salt to the brine tank.
Our Recommendation
For household drinking water, a combination of activated carbon filtration (for low tannin levels and taste improvement) and reverse osmosis (for comprehensive water purification) are often ideal.
An anion exchange system is suitable for whole-house systems, especially in areas with moderate to high tannin levels.
Chlorination is less practical for home use due to the complexity of injecting chlorine into your home’s incoming water supply. Ultra-filtration is equally impractical for home use.
Interested in delving deeper into various water treatments? Expand your knowledge using these additional resources:
In a 5 stage RO unit, which filter tends to clog up and slow the flow first? Wondering if changing only the sediment filter (easier and cheaper) extends the cycle for the more expensive filters (tannin filter is pricey).
Hello Dennis, This is a very good question. I can say with 100% confidence that the first filter in the series of filters will be the first cartridge to get clogged. This is normally a sediment filter. It will capture suspended particles but the other thing that happens is it gets coated with naturally occurring bacteria. Even with chlorinated tap water, eventually the inside of the filter canister and the sediment filter will get slimy from bacteria. This is normal and happens with just about all home water filters.The cartridge will have a reduced flow rate due to these factors. I change my sediment filter every 6 months. When I was using a spin-off filter housing I could feel the slime inside the housing. I would soak the canister with water containing about a teaspoon of bleach. After an hour I would scrub out the canister with a bottle brush. You can use dish detergent after bleaching. I am now experimenting with a counter-top RO system. The cartridges are sealed, meaning you simply twist off the filter and replace it with a new filter. You’ll never be able to notice the slime build-up. That is why I change it every 6 months. It really helps keep the flow rate up.