Disinfection By-products
Trihalomethanes and Haloacetic Acids
What are Trihalomethanes (THMs) and Haloacetic Acids (HAAs)?
THMs and HAAs are two types of disinfection by-products (DBPs). DBPs are created when water is treated with chlorine and organic matter is present. THMs and HAAs are used as indicators for the production of other DBPs. If the level of THMs and HAAs are monitored and controlled, we can expect that other DBPs, known or unknown, are also controlled.
Why add chlorine to water?
Chlorine is an essential step in the water treatment process because it kills microorganisms which can make people sick. When water is obtained from a source which contains natural organic matter, such as a lake or river, the treatment process removes most of the organic matter but it is impossible to remove it all. The organic matter which remains reacts with chlorine to produce disinfection by-products including THMs and HAAs.
Chlorine serves not only to kill microorganisms found in the source water, but also to prevent the regrowth of microorganisms, biofilm formation, and to prevent water from becoming recontaminated as it travels through underground distribution pipes from the treatment plant to your home or business.
What levels of THMs and HAAs are acceptable in water?
The Ontario Drinking Water Quality Standards specifies the maximum acceptable concentration (MAC) for microbiological, chemical, and radiological parameters in drinking water in Ontario.
The MAC for THMs and HAAs is 100µg/l and 80µg/l respectively, and is calculated as a running annual average. This means that water is sampled and tested for THMs and HAAs every three months and the past four results are averaged. A running annual average is used because the formation of THMs and HAAs can vary considerably on a seasonal basis.
How are elevated disinfection by-products detected and reported?
DBPs are an unavoidable consequence of the addition of chlorine to water containing organic matter. Water treatment plant operators endeavor to optimize the amount of chlorine added and the effectiveness of the filtration processes to minimize DBP formation. Water is sampled and tested for THMs and HAAs on a quarterly basis. Should it exceed the maximum acceptable concentration, users are notified by Peterborough Public Health and the Ministry of the Environment, Conservation, and Parks works with the system operator to find ways to reduce the formation of DBPs.
What can be done to reduce DBPs in water?
As a homeowner, you can reduce the level of DBPs in the water you consume by using an activated carbon filter. These can be whole-home, faucet-mounted or in a water pitcher. The filter must be NSF certified and changed according to the manufacturer’s recommendations.
The Ministry of Environment, Conservation, and Parks will work with the owner/operator of a Drinking Water System to determine possible causes of elevated DBPs in drinking water and assess strategies for further reduction. More information about possible strategies are outlined in Ontario’s Strategies for Minimizing the Disinfection By-Products Trihalomethanes and Haloacetic Acids document.
What are the health effects of THMs and HAAs in drinking water?
There is concern that long-term exposure to elevated levels of THMs and HAAs may pose a risk to human health, however evidence varies and research is ongoing. Certain types of these disinfection by-products have been classified by the International Agency for Research on Cancer as “possibly carcinogenic to humans”, while others have not. Some studies have shown potential adverse reproductive effects, although the evidence is inconsistent. These potential health risks must be weighed against the significant risk of water borne illness from water that has not been properly disinfected.