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HAA5 in Drinking Water: Information for Consumers

Information about Haloacetic Acids in Drinking Water (Rev. Jan. 2018)

What are HAA5?

Haloacetic acids (HAA) are a group of disinfection byproducts that form when chlorine compounds that are used to disinfect water react with other naturally-occurring chemicals in the water.  There are five significant HAA potentially found in disinfected drinking water and their combined concentration is referred to as total HAA5.

Levels of HAA5 can be affected by seasonal changes in source water quality or by changing amounts of disinfection added.  Water systems often can experience temporary increases in HAA5 due to short-term increases in chlorine disinfection.  Chlorine disinfection increases can occur when there is a water main break, when water systems are under repair, or when there is a potential microbial (example:  bacteria) problem or threat.

All water systems that use chlorine to disinfect the water are required by federal and state law to sample for HAA5 on a regular basis (quarterly, or once every three months).

Why is chlorine added?

Chlorine is used to disinfect drinking water.  Disinfection of water supplies is necessary to prevent illness and is a federal and state requirement.  The practice of disinfection has nearly eliminated most acute waterborne diseases in the United States. 

Disinfection of the water first kills any microorganisms that it may contain.  Then, a small amount of disinfectant is needed in the water as it travels through the pipes in the distribution system.  This prevents regrowth of microorganisms, or contamination from an outside source, such as during a water main break.

What is the Drinking Water Standard for HAA5 and how is compliance determined?

Drinking water standards are called Maximum Contaminant Levels (MCLs).  MCLs are set to limit risks to people from chemicals in drinking water.  Some MCLs limit the daily amount consumed (for chemicals that pose an immediate risk), and some limit the amount averaged over a long period of time (for chemicals that pose a long-term risk).  The HAA5 MCL is set at a level that balances the immediate risk of bacterial contamination should the water not be adequately disinfected and the long-term risk of health effects, such as cancer, potentially associated with long term exposures to HAA5.  The USEPA and MassDEP have set an MCL for HAA5 of 60 parts per billion (ppb) or micrograms per liter (ug/L) as an annual average.  Federal and state compliance with the MCL requires that the running annual average of four samples (i.e., quarterly, or once every three months over a year) not exceed the MCL at each sampling location.

How can consumers be exposed to HAA5 in drinking water?

The main source of exposure to HAA5 in drinking water is from ingestion (i.e., drinking the water and ingesting it in foods and/or ice prepared with the water).  It is possible that small amounts of HAA5 could be absorbed through the skin during handwashing and showering.  Significant inhalation exposures during handwashing or showering of HAA5 chemicals does not occur as these chemicals do not readily vaporize into the air.

What are the health risks associated with using water containing HAA5?

The MCL for HAA5 is based on potential cancer risks following a lifetime of drinking the water.  HAA5 are considered to be possibly carcinogenic to humans by USEPA because of evidence of carcinogenicity in experimental laboratory animals and limited evidence in people.  Some of the individual chemicals that comprise HAA5 have also caused other effects in experimental laboratory animals following high levels of exposure, including toxicity to the liver, kidneys, neurological and reproductive systems.  Various adverse reproductive and developmental effects have been observed in experimental laboratory animals following exposure to disinfection byproducts (which include HAA5).  In some, but not all, studies in people, similar effects have also been reported.  In general, young children may be more susceptible to the effects from any chemical exposure, such as HAA5, because their ability to metabolize chemicals is not mature and because their exposures may be greater for their size than in adults.  More research is being conducted to better understand the potential risks from using water containing HAA5.

Based on the available information, long term consumption of HAA5 in drinking water above the MCL may increase the risk of certain types of cancer (e.g., bladder, colon, and rectal) and other adverse effects in some people.  The degree of risk for these effects will depend on the HAA5 level and the duration of exposure.  Consumption of water with HAA5 levels somewhat above the MCL for limited durations, for example, while corrective actions are being taken to lower the levels, is not likely to significantly increase risks of adverse health effects for most people.  Because some data indicate that disinfection byproducts may increase the risk of developmental effects, women who are pregnant or may become pregnant may wish to avoid consuming water containing HAA5 and other disinfection byproducts exceeding the drinking water standard.

If you are concerned and would like to reduce your exposure to HAA5, what can you do?

The most significant measure that you can take to reduce your exposure to HAA5 is to use bottled water for drinking or preparing beverages and food that retain water such as oatmeal or pasta.  Bottled water sold in Massachusetts must meet all federal drinking water quality standards and, if originating in Massachusetts, must also meet state drinking water quality requirements.

Where can I get additional information?

If you have concerns about your exposure, particularly pregnant women and women of child-bearing age who may be at increased risk, you may wish to seek the advice of your health care provider.