What it is:

Chloramines (combined chlorine) are produced at the water plant by reacting ammonia and chlorine.

There are three inorganic chloramines in water: Monochloramine, dichloramine and trichloramine. Monochloramine is stable in drinking water with a pH of 7 to 9. As chlorine concentration increases and pH is reduced, dichloramine and trichloramine will form. It is essential to prevent di and trichloramine formation because they are very irritating and even less effective disinfectants than monochloramine. Chloramine molecules are neutral (not ionic). After primary disinfection (e.g. free chlorine), chloramines are typically used to help prevent re-growth of bacteria and suppress the formation of disinfection byproducts (DBP) while water is being distributed to consumers.

Water utilities have been using chloramines for more than 90 years.

Organic amines produce organic chloramines by the same chemistry as inorganic chloramine formation.

Chloramines are considered a secondary disinfection for drinking water because of their low biocidal activity.

Chloramines are common elements in chlorinated swimming pool water and the odor and reported eye irritation is usually attributed to trichloramine in the water.


They are used in public water supplies to supplement chlorine disinfection. However, there are several orders of magnitude less effective biocides than free chlorine.

Monochloramine is the most effective disinfectant of the chloramines, but it reacts slower than chlorine. Chloramines remain active in water longer than chlorine.

Chlorine reacts with organic matter in water to produce DBPs, it is often replaced with chloramine, which produces fewer DBPs, but some of them may be more of a concern than those produced by chlorine. For example, chloramine will react with dimethylamine in water to produce NDMA (dimethylnitrosamine), a potent carcinogen.

Chloramines can also be reduced by nitrosamonas bacteria to increase the nitrite content of water, especially in systems with long retention times.

Health effects:

Chloramines, especially di and trichloramines, cause irritation of the eyes and nose. Water treated with chloramine is safe to drink, bathe and wash with. Some people have claimed to have suffered allergic reactions to chloramines in water, but its long usage experience casts doubts on those reports. Aggravation of asthma has been claimed in some cases. Water used for kidney dialysis patients, fish and reptiles should be treated (often with granular carbon) to remove chloramines or chlorine that may be present.

Chloramine seems to be more effective than free chlorine in suppressing Legionella bacteria growth in plumbing systems, probably because its lower chemical reactivity may allow it to penetrate biofilms more effectively.

Water treatment:

Public water systems are required to regulate the amount of chloramines they use when treating water.

Chloramines are used to reduce THM and other DBP formation and to maintain a disinfectant residual in distribution systems.

A granular activated carbon filter has been known to help reduce the amount of chloramines in drinking water.


The maximum contaminant level (MCL) is 4 milligrams per liter (mg/L) or 4 parts per million (ppm), which is well above the typical use level.



Environmental Protection Agency, World Health Organization, Lenntech Water Treatment Solutions.

Water Technology would like to thank Dr. Joseph Cotruvo for reviewing this information and providing additional content.

Dr. Cotruvo is president of Joseph Cotruvo and Associates, LLC, Water, Environment and Public Health Consultants. He is a former director of the U.S. EPA Drinking Water Standards Division.

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