Trihalomethanes in Water - How to Reduce Them in My Home

by Lauren


We have been informed by the city that we have an unacceptably high level of THMs in our water. I would like your advice on filter systems to protect us and reduce exposure on all sinks and bathrooms.


The quick answer is that you would need to use a whole house water filter system that is NSF certified to reduce at least 90% chlorine and its by-products, such as trihalomethanes (THMs).

A whole house water system is the most effective way to reduce your exposure on ALL sinks and bathroom water fixtures in your home. Whole-house water filter systems are also the most expensive.

Other options include using a drinking water filter at your kitchen sink as well as shower and bath filters. This would be almost as effective as a whole house system with lower initial cost.

However, this plan would not remove THMs at bathroom sinks, where family members might use the water for brushing teeth, face washing, and so forth.

See below for Recommended Filters to Reduce Trihalomethanes (THMs).


For the sake of all our site visitors, here is a brief explanation about what THMs are, how they get in our water, and why they are considered a health risk.

According to the Environmental Protection Agency (EPA), trihalomethanes occur when naturally-occurring organic and inorganic materials in the water react with the disinfectants, chorine and chloramines. One example of a THM is chloroform, which is a known carcinogen.

Trihalomethanes are toxic when consumed, such as when drinking unfiltered chlorinated water. However, showering and bathing in chlorinated water may expose us to even more THMs, since the gases we inhale directly enter our bloodstream. Thus, taking shorter showers and baths can also reduce THM exposure.


The EPA sets an enforceable regulation called a maximum contaminant level (MCL) of THMs. “MCLs are set as close to the health goals as possible, considering cost, benefits and the ability of public water systems to detect and remove contaminants using suitable treatment technologies.”

According to the EPA, “Some people who drink water containing total trihalomethanes in excess of the MCL over many years could experience liver, kidney, or central nervous system problems and increased risk of cancer.”

According to a clinical and epidemiological review published by the National Institutes of Health, THMs from chlorinated water have been associated with spontaneous abortion, low birth weight and birth defects.

Exposure to chlorine vapors, including THMs, especially while showering and bathing, are connected to greater risk of asthma, and may harm the lining of the respiratory tract.


The EPA recognizes Granular Activated Carbon (GAC) as the best available technology for filtering trihalomethanes in water, along with other Volatile Organic Chemicals (VOCs) and synthetic chemicals.

I am not aware of any NSF certified system that offers 100% removal of THMs. There may be quite a few filter systems with multi-stage filtration that include activated carbon or something comparable, which remove over 95% THMs.

The main thing you want to look for are water systems that have multi-stage filtration and are NSF certified to remove at least 90% of chlorine, which will also reduce the chlorine by-products, such as the THMs.

The water filter systems that I am most familiar with and recommend because of their NSF certifications as well as customer feedback are the Aquasana water systems.

For example, the Aquasana EQ-600 Rhino whole house water system is NSF tested and certified to remove 97% chlorine and its by-products and is good for 600,000 gallons or about 6 years.

Their drinking water filters (countertop and under sink) use advanced filtration technologies that include Granular Activated Carbon, ion exchange and adsorption and remove over 95% of THMs.

The NSF-certified Aquasana shower filters are also high quality and remove over 90% of THMs.


I am not a big fan of reverse osmosis systems for a number of reasons, mainly because they remove naturally occurring minerals from the water and they also waste a considerable amount of water. In addition, I believe there are other water filter systems that are more effective at removing unhealthy contaminants, including THMs.

In fact, the RO membrane alone will not remove chlorine and its by-products. However, some of the whole house RO systems use multi stages of filtration media, which often includes activated carbon and will thus reduce THMs.

If one prefers an RO system, I highly recommend getting one that has multi-stage filtration and contains the activated carbon media or some other media that is certified to remove at least 90% of chlorine and THMs. I also highly recommend looking for an RO system that also has a remineralization element.


American Journal of Epidemiology; Bladder Cancer and Exposure to Water Disinfection By-Products through Ingestion, Bathing, Showering, and Swimming in Pools; 2006.

National Institutes of Health; Chlorination disinfection byproducts in water and their association with adverse reproductive outcomes: a review; 1999.

Further reading

Shower and Bath Filters

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