Chloroform, also known as trichloromethane, is a common organic chemical sometimes found in public water supplies. This colorless liquid is one of the four chemicals classified as trihalomethanes (THMs), a group of compounds regulated in drinking water.
How Chloroform Enters Drinking Water
Chloroform’s presence in public water systems is primarily a consequence of water disinfection practices designed to protect against waterborne pathogens. It is classified as a Disinfection Byproduct (DBP), formed when chlorine is introduced to disinfect the water supply and reacts with naturally occurring substances in the source water.
The chemical mechanism involves chlorine reacting with natural organic matter (NOM), such as decaying vegetation and soil runoff. These reactions generate a mixture of THMs, with chloroform often being the most abundant component. Several factors can increase the rate of chloroform formation, including higher water temperatures, increased pH levels, and a greater concentration of organic matter in the source water.
Federal agencies mandate limits for Total Trihalomethanes (TTHMs). Prolonged exposure to TTHM levels above the established maximum contaminant level (MCL) is associated with potential health issues. The chemical is classified as a probable human carcinogen, linked to potential damage to the liver, kidneys, and central nervous system. Exposure to chloroform in water is not limited to ingestion, as the chemical can also be absorbed through the skin or inhaled as vapor, such as during showering or bathing.
Practical Methods for Home Removal
Activated carbon filtration is the most reliable and widely accessible point-of-use (POU) treatment method for reducing chloroform exposure at the tap. Activated carbon works through adsorption, trapping volatile organic molecules within the filter’s highly porous structure. The effectiveness of a home filter depends on the amount of carbon it contains and the length of time the water remains in contact with the media.
Activated carbon filters are available in two main forms: granular activated carbon (GAC) and carbon block filters.
Granular Activated Carbon (GAC)
GAC filters consist of loose granules, which allow for a higher flow rate but offer less contact time for adsorption.
Carbon Block Filters
Carbon block filters are made of compressed carbon powder, creating a denser material that forces the water through a finer matrix. This structure results in a longer contact time, generally making carbon block filters more effective at removing chloroform and other THMs than GAC systems.
Another home removal strategy relies on chloroform’s volatile nature, as it readily transitions from water into the air. Simple aeration, such as pouring water between two containers, can allow a portion of the chemical to off-gas. While this process removes chloroform during activities like showering, it can also lead to inhalation exposure in a poorly ventilated bathroom.
Boiling water is not a recommended method for eliminating chloroform, although it is often used for pathogen removal. While heat causes the chemical to volatilize, the process also concentrates any non-volatile contaminants remaining in the water. Furthermore, boiling indoors without proper ventilation allows the rapidly escaping chloroform vapors to be inhaled, increasing overall exposure.
Large Scale Water Treatment Solutions
Municipal water treatment plants employ several advanced strategies to manage chloroform and other trihalomethanes before the water reaches the consumer. The most fundamental approach is precursor removal, which involves removing the organic matter from the source water before any chlorine is added. This is accomplished using enhanced coagulation or advanced filtration techniques to lower the concentration of NOM that could react with the disinfectant.
Once chloroform has already formed, treatment plants can utilize large-scale versions of the same processes available to homeowners. Advanced aeration, often referred to as air stripping, is a common technique where water is passed through large towers while air is forced through it. This rapid, high-contact aeration efficiently strips the volatile chloroform from the water, reducing concentrations before distribution.
Treatment plants also employ vast beds of granular activated carbon (GAC) or specialized resins, similar to home filters but on an industrial scale. These GAC contactors are highly effective at adsorbing both formed THMs and the organic precursors that lead to their formation. Many utilities also manage DBP formation by transitioning to alternative disinfectants, such as chloramines, which are formed by combining chlorine with ammonia. Chloramines are effective at killing pathogens and produce a significantly lower concentration of THMs, although they require careful management to avoid other potential water quality issues.