Does Reverse Osmosis Remove Tannins from Water?
Written by: Gene Fitzgerald // Last Updated: Jun 2, 2023
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Have you ever turned your faucet on, and a lot of brownish water comes running out? You could be dealing with tannins.
Tannins are natural organic substances that are commonly found in water sources like wells. When water passes through decayed vegetation in swamps, bogs, and other wetlands, these organic compounds dissolve into the water and leave it with its telltale coloring.
While mostly harmless, removing tannins from water is a common challenge many face. There are some effective methods to remove tannins from water, though. Let’s see if reverse osmosis is one of them.
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Key Takeaways
- Reverse osmosis can remove tannins from water, but an accumulation of them on the RO membrane can cause premature membrane fouling.
- Tannin removal via reverse osmosis is more effective when combined with pre-treatment, including carbon and sediment filtration as applied by most RO systems for home use.
Does Reverse Osmosis Remove Tannins from Water?
Does reverse osmosis remove tannins from water?
Yes, reverse osmosis will effectively remove tannins from water due to their high molecular weight. As such, they simply won’t make it through the microscopic pores of a reverse osmosis membrane.
However, these compounds can cause RO membrane fouling, leading to reduced efficiency, as they are biological compounds. A pre-filtration step is needed to prevent this with the goal to remove any tannins before they reach the reverse osmosis membrane.
How Does a Reverse Osmosis System Remove Tannins?
Using a sediment pre-filter, carbon pre/post-filter, and RO membrane, an RO system can rid your water of 99% of all inorganic and organic matter, including tannins. RO systems that don’t have these pre-filtration steps will also remove tannins but will be at high risk of membrane fouling.
The sediment filter will first remove any more significant bits of the organic waste, and the activated carbon filter media will reduce leftover tannins by a process called adsorption, which is when the tannin compounds are trapped in the surface pores of the filter. If there are still tannins remaining in the water at this point, they will be dealt with by the reverse osmosis membrane itself via size exclusion.
Other Methods to Remove Tannins from Water
If you do not want to install a whole reverse osmosis system to rid yourself of tannins, there are other ways to deal with them.
Activated Carbon Filtration
As mentioned before, activated carbon water filters provide an excellent option for removing natural compounds like tannins. Using adsorption, which causes the contaminants in the water to stick to the media the water passes through, most tannins are left behind.
For example, a water filter pitcher with activated carbon can clear tannins from your drinking water, but it’s no fix for other tannin-stained products such as white sinks and clothing in washers. These remain at the mercy of tannins and may end up with stains and discoloration – that’s what whole house water filters are for!
Ion Exchange
Ion exchange is another water treatment method suited for removing tannins. One of the major benefits of using ion exchange for water treatment is that this type of system is often installed at the point of entry in your home to treat water for your entire household.
Chlorination (Oxidation)
An oxidizing agent like hydrogen peroxide or chlorine can be added to reduce tannin levels in water. The oxidization process breaks the tannins down into simpler compounds that can be effectively removed through sedimentation and carbon filtration.
It is important to note, however, that chlorine and tannins might have a chemical reaction, producing cancer-causing agents called trihalomethane (THMs).
Distillation
Tannins in water can also be eliminated by distillation, where water boils and transforms into steam, leaving the heavy tannins behind.
Usually, though, this is an industrial application, and the method demands significant energy and takes a long time.
UV
Ultraviolet (UV) light has the power to eliminate tannins from water by breaking them down into simpler compounds. A UV water purifier may help to reduce tannins in water; however, this method does not eliminate them entirely.
Coagulation-Flocculation
This method of filtration uses a coagulant such as aluminum sulfate or iron salts which causes tannins and other particles to clump together, making them larger. These clumps are then removed via sediment filtration.
Biological Methods
- Microbial degradation: Microbial degradation is an effective process to remove tannins from water. It involves the consumption of tannins by microorganisms, such as bacteria and fungi, to convert them into simpler, less complex compounds. These compounds can then be easily eliminated from the water.
- Phytoremediation: Phytoremediation is a green technique for removing water pollutants with the help of plants. Mother Nature has endowed certain trees, such as willows and poplars, with the incredible ability to easily absorb and break down tannins, making them a go-to solution for water tannin removal.
- Bioreactors: Bioreactors employ microorganisms to degrade tannins from water sources. Tannins in the water serve as the microorganisms’ energy source (food!), enabling them to break down to be more easily filtered.
- Algae: Algae can effectively purify water by eliminating tannins. These small but mighty organisms consume tannins as a food source, converting them into biomass that can be easily removed from water through sediment filtration.
What Are Tannins?
Tannins, large organic compounds resulting from decomposed plants and animals, are commonly present in surface waters and shallow wells. They fall into two classifications: Humic and fulvic acids.
Tannins color water differently depending on where they come from. Water may appear yellow and tea-like with an accompanying taste and odor that is not pleasant like tea is, even though tea also gets its coloring from tannins.
Tannins are everywhere, from plants to fruit and tree bark. These naturally occurring compounds in coffee, tea, chocolate, and wine provide numerous health benefits as antioxidants.
How Do Tannins Get into Our Drinking Water, and Are They Harmful?
As natural organic materials like leaves, soil, and plants decompose, surface water from rain or snow that flows over said material before seeping into water sources can introduce tannins. The mix of water and the tannins from the plant particles causes the water to become discolored and imparts an unpleasant taste.
Tannins in water are notorious for staining, leading to yellowish tints on white clothes and porcelain. Though aesthetically unpleasant and with an icky taste, tannins generally don’t pose any danger to your health, though it’s advisable to exclude tannin-laden water from washing your whites.
Where some danger may come in, tannins can hide things that may be bad for your health, like bacteria, allowing it to slip past purification methods such as UV.
Further Reading:
Effects of Tannins in Your Home
While tannins don’t have much impact on your health, they can be annoying when they’re in your home’s water supply, as these substances can dye all sorts of stuff – from staining clothes to messing up your white bathtub or sink. Plus, they can make porcelain fixtures look pretty gross if you don’t clean them regularly. Give your favorite white towels a couple of washes in tannin-rich water, and they’ll turn beige.
Tannins also bind with minerals, which can be problematic. Your plumbing system may be affected as the water becomes acidic and more corrosive. Likewise, if ingested, there is potential for mineral deficiency in the body.
Overall Water Quality
- Aside from discoloration, it’s best to avoid cooking with or drinking water with tannins, regardless of their safety.
- Bathing in tannin-stained water won’t harm you. Still, the unpleasant color and odor make it challenging to have a pleasant experience.
- Drinking water with tannins won’t kill you, but it will taste bitter and unpleasant and likely cause you to purchase bottled water instead if you don’t have a filter.
Taste
Tannins found in groundwater have a tea-like color, but their taste is nothing like the comforting brew we’re accustomed to. Comprised of 80% humic acid and fulvic acid, these compounds produce unpalatable water with a tangy, bitter flavor and musty odor.
Plumbing and Appliances
The presence of tannins in water can lead to discoloration and the accumulation of mineral deposits in plumbing systems and appliances. This, in turn, causes a decline in their efficiency and longevity.
How You Can Test for Tannins in Water
A simple way to test for tannins is to fill a glass with water and let it sit for several hours (preferably overnight). If the water is orange, it doesn’t necessarily confirm the presence of tannins since iron and manganese can also give water an orange tone. However, if there are tannins, your glass of water will be uniformly colored throughout. If iron or manganese is the issue, it’ll settle at the bottom instead.
You may want to have a laboratory run a comprehensive water analysis to further check for tannins. Iron levels must also be checked, as testing for tannins alone can result in a false positive. Labs will determine the amount of iron in your water and then subtract that from the tannin level to get an accurate reading.
Methods of tanning testing performed in a lab include:
- UV-Vis spectrophotometry uses a spectrophotometer to measure how much light gets absorbed by your water at specific wavelengths. It’s a pretty neat trick for determining tannin concentration in water.
- A Total Phenolic Content (TPC) Assay measures the total amount of phenolic compounds in a water sample, which can be used to gauge the level of tannins. The assay generally involves reacting the sample and then measuring the absorbance of the resulting solution.
- High-performance liquid chromatography can detect tannins and other components in a given sample, providing a very accurate and sensitive measurement of tannin levels in water.
If you have any thoughts about the question, does reverse osmosis remove tannins, please don’t hesitate to leave a comment below!
About the Author Gene Fitzgerald
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