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Haloacetic acids (HAA5, HAA6Br, HAA9) are a group of disinfectant byproducts that are formed when disinfectants, such as chlorine or chloramine, are used to treat water and react with naturally occurring organic and inorganic matter present in source waters. Which HAA forms depends on several factors, so HAAs are often tracked and described as groups of individual acidic compounds. As more HAAs are included in one of these groupings, the list of compounds that contain bromide increases:

  • HAA5 includes: dibromoacetic acid, dichloroacetic acid, monobromoacetic acid, monochloroacetic acid, trichloroacetic acid
  • HAA6Br includes: bromochloroacetic acid, bromodichloroacetic acid, dibromoacetic acid, chlorodibromoacetic acid, monobromoacetic acid, tribromoacetic acid
  • HAA9 includes: bromochloroacetic acid, bromodichloroacetic acid, chlorodibromoacetic acid, dibromoacetic acid, dichloroacetic acid, monobromoacetic acid, monochloroacetic acid, tribromoacetic acid, trichloroacetic acid
The primary way people are exposed to HAAs is by ingesting disinfected drinking water. There is not a significant risk of haloacetic acids present in water being absorbed through the skin.
Data from research studies indicate that several HAAs, e.g., dichloroacetic acid and trichloroacetic acid, may be carcinogenic in laboratory animals. Exposure to other HAAs has also been associated with reproductive and developmental effects in laboratory animals. The current Maximum Contaminant Level (MCL) set for HAA5 is because of concern that exposure to HAAs over many years may increase the risk of cancer.
The best way to know if haloacetic acids are found in your drinking water is to contact your water utility or state public health agency. HAA5 is monitored regularly in all water systems that use chemical disinfectants. You can find your water system’s HAA5 monitoring results in their annual consumer confidence report. The concentration and specific HAAs present vary based on local factors including the source of water supply, the system’s disinfectant practices and the length of time water spends traveling in the distribution system.

If you get your drinking water from a private well and have concerns about haloacetic acids, you can have your water tested by a certified laboratory. Haloacetic acids are unlikely to be in your water unless you disinfect your well water with a chemical disinfectant and your well water contains organic matter.

Some HAAs like trichloroacetic acid are used in industrial applications or wastewater treatment processes and may be present in groundwater or surface water from these sources. You can find information on how to sample for haloacetic acids, and where to send samples for analysis, by contacting your state water laboratory certification officer. Contact information for your state can be found on the U.S. Environmental Protection Agency’s laboratory certification page on the UCMR4 laboratory list. Additional information about well water testing from EPA is available on their private drinking water well FAQ page.

Following the Safe Drinking Water Act Amendments of 1996, EPA set standards for HAA5 in a series of regulations (Disinfection Byproducts Rule Stage 1 and 2). The federal enforceable standard for HAA5 is a maximum running annual average for each monitoring location of 60 micrograms/liter.
If you are concerned about haloacetic acids in your drinking water, you may consider purchasing a home treatment device. However, to make a well-informed and cost-effective decision, consider:
  • Checking with your water system or consumer confidence report to learn about the amount of HAA5 in your water, and
  • Identifying a device that has been independently certified to remove haloacetic acids.

NSF International, the Water Quality Association, Underwriters Laboratories and CSA International all certify home treatment products for removal of contaminants. The relevant haloacetic acid removal standards are NSF/ANSI Standards 42 & 53. If you choose to use a home treatment device, it is very important to follow the manufacturer's operation and maintenance instructions carefully to make sure the device works properly.

Bottled water in the United States is regulated by the U.S. Food and Drug Administration and is required to meet standards equal to EPA’s tap water standards. There are also individual state standards. However, in most cases, you must contact the bottled water manufacturer for information about haloacetic acid levels.