Do you have tannins in your drinking water? If so, you may be wondering if carbon filters can remove these compounds.
Carbon filters can remove tannins from drinking water. In most cases, carbon removes 99% of the tannins. However, tannins are a group of compounds, and carbon adsorption treats some of them better than others. In addition, some brands of carbon have higher removal efficiencies than others.
In this blog post, we explore tannins and how well activated carbon works to remove them. It’s a complicated issue, and we review all of the nuances to give you a better understanding of how to solve this challenge.
What Are Tannins
Tannins are large molecular weight organic compounds. They are produced by the natural decomposition of plants and organic material. These compounds are generally found in surface waters or shallow wells.
Tannins are a group of compounds that fall within two primary categories: humic acid and fulvic acid. These are simplified structures of very large molecules. The specific tannin compounds vary from region to region, depending on the vegetation in that area.
Tannins are plant-based compounds that can give water a yellow to dark tea color. They may also impart a bitter taste and musky odor. If you enjoy wine or are familiar with the wine-making process, you may be aware of tannins.
How do tannins get in my water
Tannins are formed when vegetation and plant matter decays. They’re most likely to be found in low-lying areas, as well as marshes and seacoasts. Once created, they seep into surface water and shallow groundwater.
If you have a shallow drinking water well, your drinking water is susceptible to tannin contamination. For homes that get their water from a pond or stream, tannins may also be an issue.
Health concerns over tannins
Fortunately, tannins do not pose a health risk. They do, however, present an aesthetic problem.
The presence of tannins may give water an unpleasant taste or odor. Most people describe the taste of tannins as bitter or metallic. It is sometimes compared to strong tea.
The brown colored water can also stain your plumbing fixtures and your laundry. Tannin acts like a dye and can permanently stain your clothes. In some cases, laundry can be left with a musky smell.
While there are no health concerns associated with tannin-contaminated water, it makes it difficult to enjoy your home. Some people may be more sensitive to the taste and odor of tannins than others. It can cause an upset stomach in some people.
Drinking water standard for tannins
There are no drinking water standards for tannins. The US EPA considers tannins to be a secondary contaminant. This means they are not regulated.
Secondary drinking water standards are based on aesthetic effects (such as taste, odor, or color) in drinking water. For tannins, the standard is based on color.
Most public drinking water supplies remove tannins during the disinfection process. The addition of chlorine oxidizes the organic compounds, and they are removed through settling or filtering.
If you have a private well, the EPA standards do not apply. You are responsible for making sure your water is safe to drink.
Activated carbon adsorption is an effective and reliable water treatment process. It is considered a best available control technology by the USEPA and is a benchmark for other water treatment methods.
Carbon filters are widely used in residential and commercial water treatment systems to remove a variety of contaminants including taste and odor, chlorination byproducts, VOCs, and THMs.
Read my comprehensive Carbon Design Guide for a detailed explanation of this treatment technology.
How carbon adsorption works
Adsorption is a physical process where contaminants are removed from water by binding to the surface of the carbon media. Adsorption is different than absorption. Adsorption, which is how carbon filters work, is a physical attraction that attracts a contaminant to the surface of the carbon.
Absorption is a bulk process where the substance is taken into (absorbed) the media like a sponge. Adsorption onto activated carbon works because most organic molecules have a natural affinity for carbon. This means they will stick to the surface of the carbon. To increase the surface area available for adsorption, thousands of tiny pores are created by “activating” the carbon.
Carbon filter components
Carbon filters for residential applications are very simple. They include either a vessel filled with activated carbon (for whole-house systems) or a cartridge that contains carbon (point-of-use filters).
Granular activated carbon, also known as GAC, is the most commonly used type of carbon. GAC looks like the gravel in an aquarium. Some carbon filters include a particle pre-filter to remove sediment and suspended particles. This protects the carbon from fouling and extends the life of the media.
Many carbon filters, especially whole-house systems, include a bypass valve to allow the flow of water when the vessel is being serviced. Pressure gauges are often installed on the inlet and discharge side of the filter to allow you to monitor the amount of fouling that has occ
Types of granular activated carbon
Carbon is formed by converting organic materials like wood and coal into charcoal. The charcoal is then activating by exposing it to high temperature steam.
1 – Coal-based carbon
Most of the activated carbon used in water treatment is made from coal. The two main types use in carbon are bituminous coals and lignite coal. Coal-based carbon is very hard with pore sizes that make it ideal for removing many of the contaminants found in drinking water.
2 – Coconut shell carbon
Coconut shall carbon is highly prized for its ability to purify air and to remove difficult contaminants like PFAS and lead. This carbon is made from coconut husks. Coconut shell carbon is more expensive than coal-based carbon, but it lasts longer and is more effective at removing certain types of contaminants.
3 – Catalytic carbon
Catalytic carbon is activated carbon that has been modified through the addition of iron-hydroxide or through an enhanced activation process. It has several advantages over conventional carbon including a higher affinity for chlorine and chloramines.
How Well Does Carbon Remove Tannins
Activated carbon has a high to moderate affinity for tannins. As a result, carbon filters can remove a relatively high amount of tannins from drinking water. However, some tannins are only moderately adsorbed to carbon, so you will have to replace the media more frequently depending on which compounds are in your water.
How much tannins can carbon remove
Experience indicates that carbon filtration can remove 99% and more of tannins from drinking water. Carbon performs very well with large molecules – most tannin compounds are large.
However, some of the humic and fulvic compounds do not have a high affinity for carbon. As a result, some of these smaller molecules may pass through the carbon bed. This results in partial treatment where you’ll notice a slight yellow or brown tinge to the water.
Type of carbon is important
The brand of activated carbon you use is important. Carbon made from coconut shell is able to remove tannins very well. Some of the coal-based carbons have a moderate to high adsorption capacity.
For best performance, you should use coconut shell carbon to remove tannins from your drinking water.
Good carbon system design requirements
In order to get the best results, your carbon filtration system should be designed to the highest standards. A good design for carbon treatment of tannins should include:
- two carbon filters plumbed in series
- a sediment filter upstream of the carbon filter
- coconut shell carbon
In addition to a proper design, you need to maintain your carbon system to achieve high treatment efficiency. This includes:
- replace the sediment filter every 2 to 3 months
- change the carbon at least once per year
Testing your water for tannins
You can test your drinking water for tannins using a simple test. Fill a clear glass or jar with water and let it sit out overnight.
If the water is discolored in the morning, you have tannins. If the water is clear with sediment in the bottom, then your problem is iron or manganese.
You can also use a home test kit to measure for tannins. This would give you a definitive answer, but I don’t think it’s necessary.
Factors to Consider with Carbon Filters
If you are considering a carbon filter for your home, there are some factors you should keep in mind before making a decision.
A carbon filter can be installed as a point-of-use (POU) unit or as a whole-house system. Whole-house systems are also known as point-of-entry (POE) systems.
POU systems are less expensive to install, but they only treat water at the sink where they are installed. Whole-house systems are more expensive to install, but they will treat all of the water in your home. Typical installation costs for POE carbon filtration are between $1,300 to $5,000.
The biggest cost is the labor to install the filter. If you’re handy, you can install the system yourself. An under-sink carbon filter can be installed for less than $100. However, a filter this small would not remove all of the radon from your water.
Carbon filters require maintenance to keep them operating properly. The primary maintenance is replacement of spent carbon – spent carbon is media that has no remaining adsorption capacity.
Small, under-sink filters need to be replaced every few months. Large whole-house filters can last for 6 months to as long as 2 years before they need to be replaced. Often, the carbon will become fouled with sediment or biological growth which would require replacing it more frequently.
For a whole-house carbon unit, you have to remove the carbon from the filter vessel. This is difficult to do and, most people hire a specialty company to do this.
How often do I need to change the carbon
You need to replace the carbon when it becomes spent. This is the point where the media can no longer remove the contaminant from your water. For a typical residential system, a carbon filter has a service life of 6 months to 1 year. If your carbon becomes fouled with solids or biological growth, you may have to replace it sooner than this.
How much do replacement filters cost
POU carbon filters have a carbon cartridge that is replaced when the media is spent. The cost of an under-sink carbon cartridge is $30 to $350, depending on the size of the unit.
Whole house carbon filters require removing the spent carbon and adding fresh media to the vessel. The cost for this service is $1.40 top $4.50 per pound. A typical whole-house carbon system contains between 100 and 400 pounds of carbon – the cost for this service varies from $140 to more than $2,000.
Whole-house versus under-sink
You have two options when it comes to carbon filtration – whole-house and under-sink. Whole-house systems treat all of the water entering your home. They are more expensive to install, but they provide clean, safe water to every faucet and shower in your house.
Under-sink systems are less expensive to install, but they only treat the water at the sink where they are installed.
If you are planning to install a carbon filter for your home, you should look for NSF certification. The NSF certification mark means that the water filter has been tested for safety and to verify the manufacturer’s claims. Here are the NSF certifications that apply to caron filters:
- NSF/ANSI 42: Certified to reduce aesthetic impurities such as chlorine and taste/odor.
- NSF/ANSI 53: Certified to reduce a contaminant with a health effect. Health effects are set in this standard as regulated by the U.S. Environmental Protection Agency (EPA) and Health Canada.
- NSF/ANSI 401: Certified for emerging contaminants.
Treatment Technologies That Remove Tannins
In addition to activated carbon, two other technologies can be used to remove tannins from drinking water – reverse osmosis and ion exchange.
Reverse osmosis to remove tannins
Reverse osmosis (RO) is a membrane separation technology that removes dissolved molecules from water. It works by passing water through a semipermeable membrane. The pores in the membrane are small enough to remove tannins, but large enough to allow water molecules to pass through.
RO is very effective at removing tannins from drinking water. You can remove 99% or more of the tannin compounds from your drinking water.
However, reverse has some drawbacks. Tannins tend to foul the RO membrane. This fouling requires frequent cleaning and, eventually, you will have to replace the membrane. This can increase the cost significantly.
Ion exchange to remove tannins
Tannin compounds can be remove using ion exchange. The same resin that is used in water softeners can be used to remove tannins. The resin beads are charged with sodium ions. As the water flows through the resin, the tannin molecules are attracted to the beads and are removed from the water.
Ion exchange is very effective at removing tannins, but it has some drawbacks. The capacity of water softener resin for tannins is lower than it is for hardness. Remember – removing hardness is the primary purpose of your water softener.
This means that you will have to set your water softener to regenerate more frequently than it would for softening.
Does reverse osmosis remove tannins?
Reverse osmosis is very effective at removing tannins from drinking water. RO can remove 99.9% of all tannins from water. However, tannins can foul the semi-permeable membrane that filters out this contaminant. This results in higher maintenance costs because the membrane has to be cleaned or replaced sooner than normal.
Does bottled water contain tannins?
Bottled water does not contain tannins. Manufacturers remove this compound because it imparts a yellow or brown color to the water. No one would buy dirty looking water!
Does a refrigerator water filter remove tannins?
Refrigerator filters can remove tannins from drinking water. However, they have limited capacity to remove this impurity and you would have to replace the filter more frequently than the manufacturer recommends.
Do Brita filters remove tannins?
Brita filters can remove tannins from drinking water. However, owing to their small capacity to remove this contaminant, you will have to change the filter more frequently than Brita recommends.
Does boiling water remove tannins?
Boiling water does not remove tannins from drinking water. Tannins are relatively stable at elevated temperatures, and they are not destroyed by boiling. They do not evaporate out of the water either.
Tannins are a common problem in private wells. If you have tannins in your water, you can treat it with an activated carbon filter. Coconut shell carbon is the most effective at removing tannins from water. Be sure to use a high-quality carbon and design your system according to best practices to achieve optimal treatment results.