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What are Haloacetic Acids (HAAs) in Drinking Water?

Haloacetic acids are a group of the following 5 chemical compounds that occur in water that contains chlorine.

  • Monochloroacetic acid (MCA)
  • Dichloroacetic acid (DCA)
  • Trichloroacetic acid (TCA)
  • Monobromoacetic acid (MBA)
  • Dibromoacetic acid (DBA)

When chlorine is added to water it reacts with organic matter present in the water resulting in the formation of hundreds of chemical compounds called chlorination byproducts. Although these byproducts are not yet well understood, they are known to be toxic. Only 9 of them are regulated. The HAAs listed above are 5 of these 9 regulated byproducts of chlorination. The remaining 4 are Trihalomethanes (THMs).

Although these 5 HAAs are monitored individually, they are regulated as a group. In other words, federal guidelines for the maximum acceptable concentration of HAAs are based on one limit for all 5 HAAs combined. You will sometimes see reference to HAA5.

Maximum acceptable concentrations of HAAs in tap water

    0.8 milligrams per litre (80 parts per billion)
    This is a guideline. It is not enforced.
  • EPA (USA)
    0.06 milligrams per litre (60 parts per billion)
    In the USA, this limit is enforced.

HAAs are linked to liver cancer. 

Haloacetic acids are linked to liver cancer and negative health effects for kidneys and testes. Dichloracetic acid (DCA) is classified as probably carcinogenic to humans.

Health Canada’s maximum acceptable concentration target for Dichloracetic acid (DCA) is 0.01 milligrams per litre which is 10 times less than the 0.1 mg/L guideline for all HAAs combined. This is based on an annual average of quarterly samples. The EPA’s goal for DCA is zero.

The formation of HAAs is difficult to control in chlorinated water.

Water quality reports show that these targets are difficult to achieve in locations supplied by surface water (lakes, rivers, creeks), even by world class water treatment systems with sophisticated infrastructure and big budgets such Metro Vancouver's.

The best way of controlling the formation of chlorination byproducts is to remove as much organic matter as possible from water before chlorine is added. Larger municipalities may have the expensive equipment required to do so but this is unlikely for smaller communities and water districts.

Adequate chlorine levels vs minimizing exposure to HAAs in drinking water

Health Canada’s rationale is that maintaining effective levels of disinfectant in drinking water is more important than minimizing the byproducts that result from the use of that disinfectant. Regarding chlorination byproducts, Health Canada states: ‘Utilities should make every effort to maintain concentrations as low as reasonably achievable without compromising the effectiveness of disinfection’.

How to remove HAAs from your drinking water

Haloacetic acids are more difficult to remove from chlorinated tap water than THMs. They can be weakly adsorbed by carbon. The presence of HAAs in your drinking water can be reduced with a high quality carbon filter or with reverse osmosis.

NSF does not have a standard that includes HAAs

The fact that NSF does not yet have a standard that includes HAAs is indicative of the challenges of removing haloacetic acids from chlorinated water by any means.



Health Canada re HAAs

EPA Disinfectant Rules

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