Haloacetic acids (HAAs) are a group of chemical compounds that are a major concern in disinfected water supplies. Classified as Disinfection Byproducts (DBPs), HAAs are unintended substances created during the necessary process of treating drinking water. They form when chemical disinfectants, most commonly chlorine, interact with the natural composition of the source water. Because of their potential for long-term health impacts, HAAs are closely monitored by regulatory bodies.
How Haloacetic Acids Form in Water Treatment
Haloacetic acids are created when disinfectants react with naturally occurring organic matter (NOM) present in the source water. NOM consists of compounds like decaying leaves, soil runoff, and other organic materials. When chlorine or chloramine is introduced to kill harmful pathogens, a chemical substitution reaction occurs with the organic carbon molecules, resulting in HAA formation.
The water system environment heavily influences the amount of HAAs produced. Higher water temperatures accelerate the chemical process, increasing byproduct formation. Water with a high concentration of organic matter, typically sourced from surface water supplies, tends to produce higher levels of HAAs than groundwater. Slightly acidic water (lower pH) also promotes the production of these compounds.
The most commonly monitored and regulated haloacetic acids are a group of five compounds collectively known as HAA5. This group includes monochloroacetic acid, dichloroacetic acid (DCA), trichloroacetic acid (TCA), monobromoacetic acid, and dibromoacetic acid.
Health Effects of Long-Term HAA Exposure
The primary concern regarding haloacetic acids centers on the effects of chronic, long-term exposure. HAAs are easily absorbed into the bloodstream when ingested through drinking water. The health risks are associated with cumulative exposure over many years, as these compounds do not cause immediate, acute illness at municipal water concentrations.
Research has identified specific HAAs, such as dichloroacetic acid (DCA) and trichloroacetic acid (TCA), as agents that can cause liver tumors in laboratory animals. Epidemiological evidence suggests a possible link between long-term exposure and an increased incidence of bladder cancer in humans. The U.S. Environmental Protection Agency (EPA) considers DCA and TCA to be potential human carcinogens based on the available animal data.
Chronic exposure to HAAs has also been associated with developmental and reproductive effects. High concentrations in animal studies have been linked to developmental issues, including lower growth rates and malformations of the heart and kidneys. Some human studies have found an association between increased DBP exposure and growth deficits in newborns, such as lower birth weight. The liver, kidneys, and nervous system have also shown toxic effects in animal studies involving high HAA concentrations.
Regulating HAAs: Maximum Contaminant Levels
To mitigate public health risks, the U.S. Environmental Protection Agency (EPA) established a regulatory framework under the Disinfectants and Disinfection Byproducts Rules. This framework sets a binding standard called the Maximum Contaminant Level (MCL) for the regulated group HAA5. An MCL represents the maximum permissible level of a contaminant in water delivered to any user of a public water system.
The MCL for the sum of the five regulated haloacetic acids (HAA5) is 60 parts per billion (ppb), or 0.060 milligrams per liter (mg/L). Public water systems must monitor and test their water regularly for HAA5 concentrations. Compliance is determined by calculating the running annual average of all samples taken at each monitoring location, not by a single test.
Water systems typically collect samples quarterly over a one-year period to determine this average. The running annual average accounts for natural fluctuations in HAA levels that occur seasonally due to changes in source water quality or temperature. The regulatory standard applies to the municipal treatment and distribution system, ensuring the water delivered meets the required safety benchmark.
Home Filtration and Reduction Strategies
Consumers who wish to reduce HAA exposure beyond municipal treatment levels have several options for household filtration. Point-of-Use (POU) devices, which treat water at a specific tap, are generally the most effective solution. Granular Activated Carbon (GAC) filters are widely recognized for their ability to adsorb and reduce HAA levels.
Reverse Osmosis (RO) systems are another highly effective method, using a semipermeable membrane to filter out a wide range of contaminants, including HAAs. When selecting a system, choose products certified by an accredited organization to ensure they are designed to remove these specific byproducts. Regular replacement of filter cartridges is necessary to maintain effectiveness.
Certain non-filtration practices can also help minimize exposure. Boiling water is not an effective way to remove HAAs and can actually concentrate the compounds as the water evaporates. Consumers should also avoid drinking or cooking with hot tap water, as the elevated temperature can lead to higher concentrations of contaminants.