Is your once-clear well water turning brown or yellow like iced tea? You probably have tannins in your drinking water. Luckily, there’s no need to stop drinking it while you work to get it fixed. Tannins are organic molecules that are harmless to your body.
Tannins in water are common among private well owners, and their presence can sometimes be confused with the yellow color given off by iron. However, they are quite easy to remove from your water once identified.
This article provides an overview of what tannins are, how they affect your drinking water, and how you can remove them. Keep reading to learn everything you need to know about water tannins.
What Are Tannins?
Tannins—also referred to as fulvic and humic acid—are a group of biomolecules that make plants, trees, and fruits unpalatable to insects and other predators. These astringent molecules play a big role in protecting vegetation and regulating plant growth. Have you ever noticed a mouth-coating, puckery, or dry sensation in your mouth after eating an unripe fruit? Tannin molecules cause that.
How Do Tannins Enter Well 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.
There’s another, more probable, route for tannins to enter your well. Sometimes surface water, or local runoff, passes through the decayed leaves and peaty soil and absorbs all the tannins before seeping into your well through cracked well walls.
Tannins are generally more common in marshy, low-lying areas along the coast or near a body of water. As such, municipal water, as well as private wells, may deliver water contaminated with tannins. If your treated water comes from a swampy area, it might bring tannins. Treatment plants are not regulated to remove tannins.
Effects of Tannins on Drinking Water
Water 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.
Even though they are safe to consume, no one likes to drink yellow and smelly water. The off-putting appearance can discourage you from drinking water, resulting in dehydration. Moreover, well water professionals suggest that if you have tannins in your water due to runoff, there’s a high likelihood that you have bacteria as well, which, unlike tannins, is harmful. In such cases, switching to another water source might be a good idea until you can have your water tested for more harmful substances.
What is problematic is the strong staining ability of tannins. If you wash your laundry and utensils with this water, you’ll end up dyeing all your clothes and linens, not to mention your white porcelain basins and ceramic floor tiles.
High amounts of tannins can bond with alkaline minerals, making your water softer and more acidic. Consequently, acidic water can invite metallic contamination from the plumbing system, rendering the water unfit for drinking.
Tannins can also affect your pets. For example, water contaminated with tannins is not suitable for aquariums. Some species of fish cannot thrive in an acidic environment.
Tannins can react with other common water additives and contaminants. If you have both iron and organic contaminants like tannins, there’s a possibility of organic matter encapsulating iron and forming heme iron. Heme iron is tricky to remove because iron-removing systems do not detect it. It would require professional guidance to find the most suitable set of filters to treat it.
How to Test Tannins in Well Water
The discoloration caused by tannins and ferric-contaminated water is somewhat similar. Ferric oxide flakes also give the water an orange and yellow tint, like tannins. The difference is that ferric oxide flakes are bigger than tannin molecules and can be seen floating around or sedimented at the bottom. Still, it’s not a good idea to rely on appearance alone to diagnose a tannin problem. Here are a few easy methods to try instead:
- Rest test
One easy way to distinguish between tannins and ferric oxide is by filling a clear glass with tap water and leaving it to rest for five to six hours. If you have ferrous iron in your water, it will oxidize from coming in contact with the air and form orange flakes that will settle down at the bottom of the glass.
If you observe no flaky particles, you probably have tannins.
This test will not help you identify small amounts of tannins in the drinking water, however.
- Use a DIY testing kit
Another method is using a DIY testing kit for well water, which is readily available for purchase online or in home improvement stores. Tannin-testing kits are affordable and can detect 0–300 mg/L (or PPM) of tannic acid in water.
Some kits are designed to test only for tannins in the water, but I suggest you opt for a kit that can detect more than one type of contaminant. The kit will cost you no more than $150 and you can detect metals, volatile organic compounds, and sulfur, and you can even check the pH of your well water.
Home testing kits do not always give you a highly accurate result, but they help you gain some understanding of what’s in your water.
- Take a sample to a lab
It’s often hard to distinguish tannins from ferrous and ferric oxide at home.
The best way to check the tannins in your water is to send a sample or take 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 cost for lab tests start as low as $30, but to check for a multitude of substances you can expect to pay $100–$700, depending on the lab and the substances you want to detect. The results will help you get a good idea of what is lurking in your well.
Contact your nearby laboratory and ask them for sample preparation protocols. You can either test only for tannins or go for a package that covers ferrous, ferric oxide, manganese, total dissolved solids, volatile organic compounds, and sulfur to get a holistic overview. Typically, labs send the results within a week.
How to Remove Tannins From Water
If one treatment method works perfectly for your neighbors, that doesn’t mean the same will work for you. Every well has different types of contamination, and you need to do your homework before buying a filtration system.
Tannins are present in more than one form, depending on the type of vegetation they originate from.
To treat them, you need a system that caters to your household needs and cleans your water efficiently.
- Anion-exchange systems
Anion-exchange resin replaces negatively charged tannin ions in the water with chloride ions. Besides tannins, these systems can also remove nitrates and alkaline ions, resulting in a lower pH. Although the system removes tannins quite effectively, the price may be too much for some people. A good quality whole-house tannin filter can cost anywhere from $800 to $3000. The system backwashes and regenerates itself using brine water every two days. Typically, it will require 2–3 bags of salt every month and about 50–80 gallons of regenerating water in every cycle.
One downside of this system is that it starts giving off an unpleasant fish odor due to the presence of trimethylamine in the anion resin bed. The foul smell becomes more prominent if the water is hard. Regular regeneration can diminish the smell, but if water pH levels are greater than 8, the problem will resurface frequently. It’s best to pair up an ion-exchange resin with a water softener that removes hardness-causing minerals that can otherwise damage the anion bed. Although a water softener doesn’t directly remove tannins, it improves tannin absorption in the anion exchange filter.
- Activated carbon filters
Activated-carbon filters can remove low concentrations of tannins and other organic contamination. However, they are not as effective as the anion-exchange method. This system can be combined with an oxidation tank or reverse osmosis system to give the best results.
For better results, you can also go for an arrangement in which tannins are oxidized first using chlorine in a retention tank. Chlorine can effectively break down tannins and later be adsorbed by a carbon filter. However, in high concentrations of tannins, this method can produce trihalomethane—a carcinogen made by a combination of chlorine and tannins. Consult an expert before opting for such an arrangement.
An oxidation system coupled with carbon filters is an affordable route if you don’t want to spend heaps of money on removing tannins.
- 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. The semipermeable membrane is able to capture many types of suspended contaminants in water, like natural organic material, bacteria and viruses, proteins, pyrogens, and other dissolved solids. These filters are available in different pores sizes ranging from 0.005 to 0.1 micron.
UF membranes need regular maintenance to flush away the captured particles in membranes. For UF to work efficiently, you need to pretreat the water for any iron and hardness-causing molecules.
- Reverse osmosis systems (RO)
Reverse osmosis systems can effectively remove large-molecular-weight tannins in the water.
Installing a point-of-entry RO system will cost you a fortune and is not very convenient from a budget point of view. Instead, opt for point-of-use RO filters for a few taps in your home. RO systems can tackle many other contaminants, such as microbes, volatile organic compounds, metals, and hydrogen sulfide. In case you have a wide variety of toxins besides tannins, RO is your best bet.
Important: Arrangement of water filters
If you are tackling multiple contaminants, such as iron, hardness molecules, and bacteria in your water, you must pay close attention to the arrangement of your filtration systems. For example, tannin filters must always come after iron and water softeners. Never forget a prefilter before a water softener. If you’re installing the ultraviolet filter, it needs to go after the tannin filter to kill off microbes left in the water.
How to Prevent Tannins From Entering Your Wells
Toxins will always find a way to enter your private wells. But you can prevent your water from becoming a pool of contaminants by testing and maintaining your wells every six months. Keep in mind the following points to prevent contamination in your well.
Location plays a big role in determining what lurks in your well. Contaminants in your water may be entirely different from toxins in another well just a few yards away from your house.
Ideally, your well should be 100 meters away from water bodies, septic tanks, farms, cesspools, garbage disposals, and industries. Make sure there is no abandoned well within 200 feet of your location. Such wells are a nest of decaying organic matter and can severely contaminate nearby groundwater and soil.
Shallow wells are more prone to surface contamination. Before buying a new property, ensure the well has a depth of 100–150 feet. The deeper the well, the better the water quality.
You can prevent toxins from entering your well by maintaining the well casing and renovating a cracked and corroded plumbing system.
Build the head of your well at least 12 inches above the ground and tightly seal the surface to prevent local runoff from seeping into the water.
- Age of the well
Wells over 30 years old tend to have a lot of organic contamination due to the growth of shrubs, plants, and tree roots, which can create cracks and holes in the well casing. Regular maintenance can help prevent frequent contamination of water.
Before moving into a new home, make sure you test the water quality and observe the structure and location of the well. Tannins in water are not harmful to consume, but they give the water a musty odor, bitter taste, and tea like color that can stain your white fixtures and laundry.
There are a few water filter systems to help remove tannins, such as ultrafiltration membranes, anion oxidation system, chlorination followed by active carbon filtration, and reverse osmosis.
Choose the one that suits your needs the best, and if you’re indecisive, don’t hesitate to seek expert advice.