Chloramines are disinfectants used to treat our drinking water. Chloramines are formed when ammonia is added to the chlorine in our water. The purpose according to the City of San Diego is to provide longer-lasting water treatment as the water moves through pipes to consumers.
From The San Diego Water Quality Report:
"Conventional Water Treatment Process"
San Diego uses a water treatment process that is similar to other large water utilities around the nation. The process produces safe drinking water by removing potentially harmful organisms and substances both in the water and attached to particles. Raw water from our reservoirs (or outside sources) is disinfected with chlorine to kill disease-causing organisms and to remove disagreeable tastes and odors. Particles in the water have negative electrical charges and repel each other. To remove them, positively charged chemicals, ferric chloride and organic polymer, are mixed with the water to neutralize the negative charges and allow clumps of particles to form. The clumps then settle out or are filtered out of the water. Ammonia is added to the water after filtration to react with chlorine to produce chloramines. Chloramines are used to continue disinfecting the water throughout the distribution pipelines so that it remains safe to drink when it reaches the consumer’s tap. Sodium hydroxide or calcium oxide is added to the water to protect pipes, plumbing fixtures and appliances from corrosion (rust)."