Are concerned about the presence of trihalomethanes in your drinking water? If so, you may be wondering if carbon filters can remove THMs.
Trihalomethanes are disinfection byproducts that can form in water supplies that use chlorine. They are a potential health concern, which is why the EPA has set a drinking water standard for them.
Activated carbon filtration is an effective method for the treatment of trihalomethanes in drinking water. Carbon can remove 95% to more than 99.9% of all THMs from water. Achieving high removal rates of these disinfection byproducts requires a properly designed and well-maintained carbon filter system.
To find out more about how well carbon filters remove trihalomethanes and what a good carbon system should have, continue reading.
What Are Trihalomethanes
Public water supplies have been using chlorine and other disinfectants to control microbial contaminants for over 100 years. This practice has greatly improved the quality of our drinking water and reduced the spread of disease.
However, the use of disinfectants also creates new “secondary” pollutants known as disinfection byproducts (DBPs). DBPs are formed when chlorine reacts with natural organic matter in the raw water.
Of particular concern are a group of four chemicals known as trihalomethanes (THMs). Trihalomethanes consist of:
Important factors in the formation of THM include:
- the type of organic matter in the unfiltered water
- concentration of organic matter
- reaction time
- water temperature
Trihalomethanes are part of a larger class of halogenated organic compounds that are associated with public water supplies and chlorinated water. THMs are the most common halogenated organic compounds in water, and chloroform is the most common THM.
Other disinfection byproducts include halogenated acetic acids (HAA).
Health concerns over trihalomethanes
Trihalomethanes have been linked to a number of health concerns. One of the most serious is cancer. They are rated as either probable or possible human carcinogens:
- chloroform – Class B2 carcinogen (probable)
- bromoform – Class B2 carcinogen (probable)
- bromodichloromethane – Class B2 carcinogen (probable)
- dibromochloromethane Class C carcinogen (possible)
Trihalomethanes have been known to interfere with the proper function of the nervous system, liver, and kidneys. These substances can also lead to miscarriages if ingested.
You might be exposed to trihalomethanes in several ways, including:
- Drinking chlorinated water. Most Americans drink public water that is treated with chlorine or other disinfectants.
- Breathing THMs volatized from water. THMs are volatile and can be released into the air when water is aerated during showers or exposed to air.
- Contact with skin. THMs can be absorbed through the skin.
While there are health risks associated with THMs in water, they are very minor in comparison to the dangers of deadly diseases present in untreated water.
Drinking water standard for trihalomethanes
The US EPA established a maximum contaminant level (MCL) for total trihalomethanes at 80 parts per billion (ppb). A MCL is the maximum concentration of a contaminant that is allowed in drinking water. MCLs are enforceable standards.
There are no MCLs for the four specific chemicals making up THMs. These compounds do, however, have maximum contaminant level goals (MCLG). A MCLG is the concentration of a contaminant below which there is no risk to health. The MCLG is a non-enforceable public health goal that allows for a certain degree of safety.
The following table presents the MCLs and MCLGs for THMs.
|Total THMs||0.080 mg/L||NA|
|Chloroform||No MCL||0.07 mg/L|
|bromodichloromethane||No MCL||0 mg/L|
|dibromochloromethane||No MCL||0.06 mg/L|
|bromoform||No MCL||0 mg/L|
|Other Disinfection Byproducts|
|Bromate||0.010 mg/L||0 mg/L|
|Chlorite||1.0 mg/L||0.8 mg/L|
|Haloacetic acids||0.060 mg/L||NA|
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 Trihalomethanes
Carbon adsorption is very effective for removing trihalomethanes from drinking water. The US EPA recommends using activated carbon for removing THMs from potable water supplies.
How much THM can carbon remove
Activated carbon can remove 95 to 99.9% of trihalomethanes in water. The percentage of THM removal will depend on the type of activated carbon, contact time, and water temperature.
The service life of the activated carbon filter depends on:
- volume of water treated
- concentration of THMs
- specific THM compound ratio and concentration
- water temperature
Good carbon system design requirements
Carbon filtration removes trihalomethanes very effectively. To receive the maximum removal efficiency, your carbon system must be properly designed and well maintained.
A good carbon system design must meet the following requirements:
- Whole house system: It is essential to treat all of the water entering your house to fully protect your family. You can be exposed to THMs through volatilization when water is aerated in your shower or when the water contacts your skin.
- Particle filter: Water contains suspended solids that can foul the activated carbon and decrease its service life. A particle filter will remove these suspended solids and extend the life of your activated carbon filter.
- Two filters in series: To treat water to low drinking water standards (80 ppb), you need two carbon filters plumbed in series. The first filter removes all of the trihalomethanes and the second filter is a polishing unit to remove anything that the first filter missed.
- Adequate carbon: You need a minimum of 100 pounds of carbon to reliably treat all of the water entering your house.
- Flow meter: The carbon bed has a limited life, and the volume of water is the largest factor in determining how long the carbon will last. A flow meter allows you to monitor water usage. This information is used to determine when it’s time to replace the carbon bed
Carbon system maintenance
You need to properly maintain your carbon system to keep it operating at peak performance. The two most important things you can do to maintain your system are:
- Change the carbon when needed: You need to replace the carbon bed before it’s exhausted. Depending on your water usage and the concentration of THMs, this is typically every three to five years.
- Clean the filters regularly: It’s important to clean the filters on a regular basis. Depending on your water quality, you may need to clean the filters every month or two.
The carbon will eventually become saturated with THMs and other contaminants and will no longer be effective. If you follow the above design guidelines, the carbon should last for more than a year. You should still replace the carbon once a year, even if it hasn’t been used up to ensure it is still effective.
Carbon Filter Types and THM Removal
Drinking water contaminated with THMs can be purified by using activated carbon filters. There are several types of home activated carbon filters that can be used to remove trihalomethanes and other disinfection byproducts from drinking water, including:
- whole house
- faucet filters
- pitcher filters
- refrigerator filters
1 – Whole house carbon filters and THM removal
A whole house carbon filter is installed at the main water supply line to purify all the water entering your home. Whole house systems are very effective at removing trihalomethanes and other contaminants from your drinking water. A well-designed whole house system can remove up to 99% of THMs from your water.
By treating all of your water, this filter configuration protects your family from exposure to THMs from drinking, bathing, cooking, and laundry. Installing a whole house system is the most effective way to remove THMs from your water. However, this option can be expensive and may require professional installation.
2 – Under-sink carbon filter and THM removal
Under-sink carbon filters are installed under your kitchen sink to purify the water coming out of your kitchen faucet. This type of filter is less expensive than a whole house system and can be installed without professional help. However, it will only purify the water coming out of your kitchen faucet and will not remove THMs from water used for bathing, laundry, or other purposes.
Under-sink filters are very effective at removing THMs from your drinking water. A well-designed under-sink system can remove up to 99% of THMs from your water. Installing an under-sink carbon filter is a good option if you are looking for an effective way to remove THMs from your drinking water without spending a lot of money.
3 – Faucet carbon filter and THM removal
A faucet carbon filter is a small filter that attaches to your kitchen faucet. Faucet filters are the least expensive type of carbon filter and can be installed without professional help. However, they will only purify the water coming out of your kitchen faucet and will not remove THMs from water used for bathing, laundry, or other purposes.
Faucet filters are not as effective at removing THMs as whole house and under-sink systems. A well-designed faucet filter can remove 95 to 99% of THMs from your water. Installing a faucet carbon filter is a good option if you are looking for a low-cost way to remove THMs from your drinking water.
4 – Pitcher filter and THM removal
Pitcher filters, such as Brita and Pur, are popular water purification devices. These filters are ideally suited for single family homes with 1 to 4 people. Pitcher filters are extremely convenient and simple to use. They do not require installation – like faucet and whole-house filters, and maintenance is easy. Just replace the cartridge every few months as needed.
Pitcher filters are designed to remove a wide variety of contaminants from water, including chlorine taste and odor, lead, cysts, and chemicals. However, they are not effective at removing all contaminants.
Look for third party certification to ensure the filter can remove THMs and other DBPs from your water. NSF/ANSI Standards 42, 53, 401, and P473 verify contaminant reduction. Pitcher filters do not treat the water you cook and bathe with. You can be exposed to THMs in these water sources.
5 – Refrigerator filters and THM removal
Most refrigerator filters use activated carbon to remove chlorine and taste/odor compounds from drinking water. While carbon is an effective treatment method for THMs, your fridge filter most likely does not have enough of it to remove all of these contaminants.
Another limitation with refrigerator filters is the limited contact time. Contact time is the amount of time water is in contact with the carbon. The longer the contact time, the more effective the carbon will be at removing contaminants. The standard refrigerator filter is too small to remove THMs from your drinking water. They provide good-tasting water, but you should use a larger carbon filter to purify your drinking water.
Refrigerator filters do not treat all of your water. As a result, you can be exposed to THMs in other water sources in your home, like the water you bathe with.
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.
Does reverse osmosis remove trihalomethanes?
Reverse osmosis systems remove all trihalomethanes from drinking water. A quality RO system can remove 99+% of THMs. One benefit of using reverse osmosis to treat THMs is that this filter also removes a long list of other contaminants that may be in your drinking water.
Does bottled water contain trihalomethanes?
Most brands of bottled water do not contain trihalomethanes. Testing is not required for bottled water, so it’s not possible to know for sure. However, many bottled water brands treat the water using reverse osmosis and activated carbon. Both of these treatment technologies remove THMs from water.
Does a refrigerator water filter remove THMs?
Most refrigerator filters contain activated carbon which is very effective at removing THMs from water. However, these filters are too small and don’t have enough carbon to be a reliable method of purifying your water.
Do Brita filters remove THMs?
Brita, and other water filter pitchers, provide moderate removal of trihalomethanes from drinking water. In general, Brita filters are not designed for treating THMs and should not be relied on for purifying your drinking water. Only use a Brita filter that is NSF-certified for THM reduction under NSF/ANSI Standard 53.
Does boiling water remove trihalomethanes?
Trihalomethanes are volatile organic compounds, and boiling will drive them out of water. One study found that trihalomethane concentrations were reduced by 64–98% when the water was boiled. Boiling water for 1 minute reduced the concentration of chloroform by 75%.
If you’re looking for a way to remove trihalomethanes from your family’s drinking water, using a carbon filter is the most convenient and simple solution. The best type of filter is a whole house system that treats all the water in your home. This approach will protect your family from THMs in your drinking water and prevent exposure from cooking with and bathing in it.