N-nitrosodimethylamine (NDMA) is a semivolatile organic chemical that is soluble in water. The US Environmental Protection Agency has established a 10-6 cancer risk level for NDMA of 0.7 ng/L. NDMA was reported in California drinking water in 1998 at several sites. It was also found in drinking water in Canada as a potential disinfection by-product. The most recent data demonstrated that NDMA is a disinfection by-product associated with the use of chloramines.

More stringent drinking water disinfection by-product (DBP) regulations have led drinking water utilities to consider modifications in treatment processes. These modifications include the use of alternative disinfectants that produce less DBPs. Currently chloramines have been successfully used by many utilities as a primary and post disinfectant instead of chlorine to reduce trihalomethanes (THMs) and haloacetic acids (HAAs) formation. It is expected that more and more water utilities will use chloramines as a disinfectant in the future. This means that an increasing number of people will be exposed to NDMA in the drinking water. Very limited information about the NDMA formation mechanism in the drinking water treatment processes is available. This paper reviews the current knowledge of the formation and stability of NDMA.