Water can come from a variety of sources, such as lakes and wells that can be contaminated with germs that can make people sick. Germs can also contaminate water as it travels through miles of piping to get to a community. To prevent this, drinking water providers add a disinfectant that kills germs. The most commonly added disinfectants are chlorine and mono-chloramine.

At MMWD's treatment plants chlorine is added as a primary disinfectant to make the water safe from microbial and biological pathogens, germs, that may be present in the water. However, chlorine can also form disinfection by-products, some of which may be cancer causing. In order to limit the formation of these by-products, which are regulated by state and federal agencies, ammonia is added to chlorinated water in the correct proportion to form mono-chloramine.

Specifically, mono-chloramine is a long lived and very effective disinfectant that stops the formation of chlorine by-products and ensures the treated water remains free from germs and safe to drink as it flows through the distribution system to our taps.
Chloramines have been used to disinfect municipal water supplies since the 1930s. Today, many agencies in California and the rest of the country use chloramines. In California these agencies include SFPUC, EBMUD, Contra Costa Water District, and Metropolitan Water District. Many other water systems throughout the country use chloramines, most notably the Denver Water Department, which has used chloramines for more than 90 years. MMWD has used mono-chloramines since 1995. In 1998, an EPA survey estimated that more than 68 million Americans were drinking water disinfected with mono-chloramine.

According to the CDC, current studies indicate that using or drinking water with small amounts of mono-chloramine does not cause harmful health effects. These studies reported no observed health effects from drinking water with mono-chloramine levels of less than 50 mg/L, milligrams per liter, in drinking water. This is substantially higher than MMWD's typical mono-chloramine disinfection level of 1 to 2 mg/L. More information is available through the EPA.

Chloraminated water is safe for people and animals to drink and for all other general uses. However, as with chlorine, chloramine will need to be removed for fish and amphibian use, and for people or businesses requiring highly treated water.