Chloramine is a chemical disinfectant used by many municipalities to treat drinking water supplies, and its use is becoming increasingly common across the United States. It is a stable compound that provides lasting protection against waterborne pathogens as water travels through the extensive public distribution system. This disinfectant is intentionally introduced into the water supply as an alternative to or in conjunction with free chlorine to help meet federal safety standards. More than one in five Americans now receive drinking water treated with chloramines.
How Chloramine is Formed and Used in Water Treatment
Chloramine is chemically produced by carefully controlling the addition of ammonia to water already treated with chlorine. This reaction creates a group of compounds known as chloramines, including monochloramine, dichloramine, and trichloramine. Water treatment plants specifically aim to produce monochloramine, as it is the most stable and preferred species for disinfection. The concentration of the different forms depends heavily on the water’s pH, temperature, and the ratio of chlorine to ammonia used.
The primary use of chloramine is to provide a long-lasting disinfectant residual throughout the water distribution network. Chlorine, while a strong disinfectant, tends to dissipate quickly, making it less effective in the far reaches of the pipe system. Monochloramine is much more stable and can persist for days, ensuring the water remains safe until it reaches the consumer’s tap. Utilities also switch to chloramine to reduce the formation of regulated disinfection byproducts (DBPs) like trihalomethanes (THMs) and haloacetic acids (HAAs). These byproducts form when chlorine reacts with naturally occurring organic matter in the source water.
Chloramine vs. Chlorine: Understanding the Differences
The distinction between chloramine and chlorine lies in their chemical reactivity, stability, and disinfection characteristics. Chloramine is a weaker disinfectant than free chlorine, meaning it takes longer to kill microorganisms. Despite its slower action, its greater stability is a major advantage for maintaining residual disinfection across long distances in the water system. Chlorine dissipates relatively quickly, often leading to a loss of protection further down the line.
A key reason for the widespread adoption of chloramine is its impact on disinfection byproducts (DBPs). When organic matter is present, chlorine can form higher levels of regulated DBPs, which are suspected carcinogens. Chloramine is less reactive with organic compounds and significantly lowers the concentration of these regulated byproducts. However, chloramine can instead form different nitrogen-containing DBPs (N-DBPs), which are currently undergoing increasing scrutiny. Chloramine also results in fewer consumer complaints about the harsh, “bleach-like” taste and odor commonly associated with high levels of free chlorine.
Safety and Health Implications
Water that contains chloramine and meets regulatory standards is considered safe for drinking, cooking, bathing, and other household uses for the general public. The Environmental Protection Agency (EPA) has set the maximum residual disinfectant level (MRDL) for chloramines at 4.0 milligrams per liter (mg/L). The use of any disinfectant, including chloramine, is necessary to prevent the spread of infectious diseases from waterborne pathogens. This benefit outweighs the low-level risk posed by disinfection byproducts.
Certain precautions are necessary for specific groups and applications. Chloramine must be completely removed from water used in kidney dialysis machines. If chloramine enters the bloodstream across the dialysis membrane, it can cause hemolytic anemia by altering hemoglobin. Chloramine is also highly toxic to all aquatic life, including fish, reptiles, and amphibians, because it can enter their bloodstream through the gills. Water used for fish tanks or ponds must be neutralized using specialized chemical additives before use.
Some people may experience aesthetic effects from chloramine-treated water, though these are not considered health risks at regulated levels. Inhaling chloramine vapors, such as during a hot shower, can irritate the eyes, nose, and respiratory system for sensitive individuals. This irritation is more commonly associated with higher concentrations found in swimming pools. Skin and eye dryness or the exacerbation of conditions like eczema have also been reported.
Practical Methods for Removal
Removing chloramine from household water is considerably more challenging than removing free chlorine due to its chemical stability. Standard granular activated carbon (GAC) filters, which effectively remove chlorine, are largely ineffective against chloramine unless the contact time is exceptionally long. Specialized filtration media are required to reliably remove chloramine.
The most effective filtration method utilizes catalytic carbon, a modified form of activated carbon that facilitates the chemical breakdown of the chloramine molecule. For whole-house treatment, a large-capacity catalytic carbon system is the standard. Reverse osmosis (RO) systems, often used for drinking water at a single tap, can also reduce chloramine. However, they typically require a catalytic carbon pre-filter because the RO membrane alone does not effectively block the molecule.
Chemical neutralization offers an immediate solution, particularly for small volumes of water, such as those used for aquariums. Compounds like sodium thiosulfate or ascorbic acid (Vitamin C) can be added to the water to instantly neutralize the chloramine residual. Common household methods like boiling or letting water stand, which effectively remove chlorine, are not practical or effective for removing chloramine because of its persistent nature.