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THMs: Poison in Your Drinking Water?


Known properly as trihalomethanes, THM’s are produced when the chlorine that is used to “purify” drinking water reacts to with the organic matter it targets. While chlorine does kill harmful bacteria, the THM’s produced in the process are confirmed class b carcinogens and include such substances as chloroform, which is a poison that can cause respiratory or cardiac arrest and death.

What are THMs and How Do They Affect Us?

THMs are toxic chemical compounds that are essentially different forms of methanes, where three of the four hydrogen atoms on the methane molecule are replaced by halogen atoms: fluorine, bromine, chlorine, iodine or astatine. The Guidelines for Canadian Drinking Water Quality allows for just 0.1mg THM’s as a group per Litre based on the health effects of chloroform, since 2006 – though the recommended level is none at all. Groundwater sources of raw water are more likely to have higher levels of THMs because there must be organic matter present for these chemical poisons to be created. The kinds of THM’s that may be in your drinking water depend on the pH levels, humic acid concentration, temperature, pH, and bromide ion concentration (when bromide is present, chloroform concentration is reduced).


Bromoform is produced naturally by phytoplankton, but it is a known carcinogen in animals. It is found frequently in public swimming pools. This poison can be absorbed through the skin or via inhalation when showering. It can irritate the respiratory tract, the eyes, skin and may cause impaired functions of the liver and central nervous system. Bromoform is not commercially produced as much as it used to be due to its multiple health effects, but was once used as a solvent, sedative and flame retardant.


Bromodichloromethane was used as a solvent for fats and waxes and mineral separation. Now it is only used in organic chemistry. It is an irritant to eyes and skin and can cause damage to liver and kidneys through prolonged or repeated exposure. Studies in animals have produced significant evidence that this may be carcinogenic to human beings as well. Chlorodibromomethane is also considered to be a possible carcinogen.


Chloroform, probably the most recognizable THM, is often used as a solvent in organic chemistry because of its ability to dissolve organic compounds. It is produced naturally by some seaweeds and algae. Chloroform was used in cough syrups, ointments and toothpaste, but has since been banned as a consumer substance. It was once widely used as an anesthetic due to its ability to depress the central nervous system, but was abandoned when it was found to cause fatal cardiac arrhythmia. A fatal oral dose of chloroform may be as small as 10 mL. Chloroform can cause dizziness, fatigue, headache, sores, and in prolonged cases of exposure, liver and kidney damage. Studies in animals have shown that miscarriages and birth defects occur when the animal is exposed to chloroform. If these effects weren’t bad enough these same studies show that it is possibly also a carcinogen.

Only these, the most common THM’s, appear on the guidelines for water treatment. But there are other THMs that can also have a detrimental effect on health. Iodoform can irritate the eyes and skin, cause dizziness and nausea and damage the heart, liver, kidneys and respiratory system. It occurs rarely in drinking water, but can cause a slightly medicinal odour if it is present. Fluoroform‘s main hazards are listed as ‘nervous system depression’, which refers to a decreased rate of breathing, heartbeat, and loss of consciousness which can lead to coma or death. Chlorodifluoromethane and can cause cardiac disorders and depression of the nervous system. Dibromochloromethane can cause a slowing of normal brain activities in low doses, causing sleepiness, and in higher doses, death. Exposure over time can cause liver or kidney damage. All of these THMs can be absorbed through the skin while showering or bathing, by inhalation when released as a gas or orally when you drink contaminated water.

Do Water Treatment Plants Test for THMs if They’re so Dangerous?

While most municipal water treatment plants must test for THMs as per the drinking water guidelines, many do not have the budget to implement the appropriate measures to minimize or eliminate the production of THMs during the disinfection process. An alarming example of this is in Newfoundland and Labrador. The use of a volatile poison to eradicate bacteria and parasites that causes disease in humans seemed like a good idea at the time but the long term health effects of using such a noxious chemical are rapidly becoming clear.

So what can you do in the meantime? Government officials and health professionals alike agree that the use of a home water filtration system can reduce the risk of exposure to these harmful chemicals. Please don’t wait for these dangerous byproducts to damage your family, visit our store now, or contact us for more information on reverse osmosis water filtration systems and how they can help remove THM’s from your drinking water.

If you’re at all concerned about the quality of your water, or you simply want to be certain, you should choose an Aquasafe Home Reverse Osmosis System. An Aquasafe Home Reverse Osmosis system will remove all contaminants from water, including THM’s and HAA’s, producing guaranteed safe water you can count on every time. And it’s only a few cents per liter! Shop online and save today.

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