THMs In Your Drinking Water | What You Can Do About It

THMs are a carcinogenic by-product in drinking water.

What are THMs ?

What in the world are THMs and why should I care?

The short answer is Trihalomethanes. It’s a byproduct class of molecule resulting from the disinfectants used to clean drinking water.

Trihalomethanes are formed as a by-product predominantly when chlorine is used to disinfect drinking water. They are generally referred to as disinfection by-products.

So, what’s the problem? Many THMs are carcinogenic.

Before you panic, the EPA (and other governments in the developed world) regulate/limit THMs within the drinking water infrastructure.

However with that said, here’s an interesting report…

Chemicals in tap water are causing thousands of cancer deaths across Europe.

Each year, more than 6,500 cases of bladder cancer. Roughly five percent of all cases in Europe are found to be attributable to exposure to trihalomethanes (THMs) in drinking water – and it’s all perfectly legal.

source: RT

THIS concern is not just in Europe. Also, right here in North America….

While regulatory limits of chemicals / by-products in our drinking water is logically a good thing, the issue is this… Limits are just that — limits. There’s still that by-product in the water.

It’s just held to a level to which they determine to be acceptable. Acceptable? Maybe that’s simply a threshold where “x” amount of people will be affected rather than “y”. Perhaps a risk-reward threshold that’s acceptable for the majority (as an example).

So the thing is — why not mitigate it yourself?

How To Remove THMs From Your Drinking Water

The answer is simple. Get a Bereky water filter.

According to Laboratory tests, the Berkey products can remove Trihalomethane (THMs) up to 99.8% (source).

The Berkey Water Filter Systems are reportedly the best water gravity filters available in the market today. I have been utilizing their filters for well over a decade. ALL of my drinking water first runs through their elements. Even if water is deemed ‘safe’ by the EPA, why not add an additional layer of security?

Yes, USA Berkey Filters is a sponsor on this site. Why? Because I’m a strong supporter of their product. It’s not just “lip service”. I actually put my money where my mouth is, so to speak. I own their filters. Use them daily. They’re the best gravity filter system in the market, in my estimation. And THMs are yet another reason to consider having one yourself.

Continue reading: Berkey Filter Pore Size


  1. For those of us on well water, how often would you suggest we have it tested?

    1. I am also on a shallow well. Never had the water tested. But as Ken does all drinking water goes through a Berkey filter. We’ve never had any problems. These filters are money well spent.

  2. Who Knows,
    I would test your well water at least annually if you are rural, out of a town. Usually in rural areas, the county health departments can take a sample ( or a very fresh one you have brought in) and run it through a lab, (usually a State lab or a contract lab). They test for a variety of things, fecal coliform bacteria, maybe radon in those areas, but may also may check for metals (arsenic, etc.) or pesticides if they are prominent in your area. Many times it is just a basic test, so you might want to ask first what they check for. You then may want to contact a water lab in your state and see about getting a full blown water analysis done, at least initially, then use the county test annually just to make sure things are not changing.
    This is what I recommend to my friends and clients. I am what could be termed as a “water professional”.

  3. As water industry proffesional, THM’s are a byproduct from the organics found in the water. With this being said, it is a good idea to know where your water is coming from. Surface water has the greatest potential for high disinfection by products.
    Get a berkey…because these are the same people who say that asbestos causes cancer…but asbestos cement pipe which carries your water only causes benign polyps in your intestines.

    1. Thanks for your input as an industry professional. It does not hurt (but can only benefit) by filtering one’s water for drinking – even if the source is supposedly ‘good’.

  4. I’ll presume this means we shouldn’t use bleach to disinfect questionable water.

  5. As an aside, I’ve sent to requests to Berkey about the ability of their filters to remove the toxins produced by algae. I have not received a reply. I’ll be making a third request today.

  6. If you are on well water and it is not chlorinated you don’t have to worry about DBPs.

    1. Thanks for pointing that out. Yes, this applies to municipal water systems – whereby chlorination is regularly applied. Chlorination is necessary for a safe infrastructure from organic contaminants. When I’ve measured this I’ve typically seen apprx. 1 ppm, plus or minus a half… though my present home is well water — all natural.

      The article references the potential by-products of chlorination in municipal systems, which is regulated & limited. However, “better safe than sorry” is how I look at it (regarding quality filtering one’s drinking water).

  7. “Why not add an additional layer of security”, Absolutely. As for preps we use every single day as compared to those we seldom use, why not run all your drinking water through a Berkey. We have been very satisfied customers now for many years.

  8. Observation: our drains in our tub always leave a little puddle around it after showers….now, sometimes, the next day when the little puddle evaporates, an orange/pinkish stain is left.
    I thought it was something in the shampoo/body wash, etc. because my tub has never left that stain, just the man of the house’s tub.
    Once I had to use Mr. Clean Eraser (generic online for 15 ¢ each) to remove this stain. Any ideas what this is??
    I use filtered water to cook, but I’m thinking our bodies are exposed to this!!??!!

    1. JayJay
      It would be a hypnotical guess on my part. If it is only happens after your husband showers it could be a reaction to the soap/body wash used on his skin. In relationship to possibly a medication that comes to the surface of his skin brought about from sweating.
      Berkey sells shower heads for those who are on city water. fyi

    2. JAY JAY,… When I see pink in a bathroom I think of: Serratia marcescens . He could be a carrier or have it in low level. esp if he has been in a hospital.
      *****It can GROW in bleach. Wash out tub after he uses with peroxide.. allow it to sit for 5 minutes…. you can get it from the residue. This is the same pink slime that people used to see on soap,in bathrooms in gas stations.
      It is very hard to knock out. DH got it in lungs as a Hospital acquired pneumonia.. We both almost died from it. We Had to take keflex, followed by doxi with several herbals.. including pippissewa, usnea, oil of oregano and garlic. antibiotic course was 21 days. anything less it returns. and antibiotic alone will not do it.

  9. My house is on well water but the well is only 30ft. deep (South Florida Location). Soil is not clay but freakin sand.
    Water is first run through Iron Filter then a Standard Water Softener. From there We use a 5 stage reverse osmosis system last stage removes possible fecal coliform bacteria and other organics. We always get our water tested.
    I can say no issues with the RO system. Always pass the water quality tests.

    We use the U.S. Water Systems. 5 stage RO.

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