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Drinking Water Disinfection - Chlorine and Chloramine

It is common practice throughout the developed world to disinfect drinking water as part of the treatment process. It may be hard to believe, water has the potential to spread devastating diseases. Historically, waterborne diseases have killed millions of people throughout the world. Even today, thousands die each year in underdeveloped regions of the world due to poor water quality.


Multiple Barriers

Water systems generally use multiple barriers to prevent contamination of their water systems. Anaheim, like other water systems, utilizes high quality source water, maintains a tight water distribution system, tests its water regularly, and has programs in place to prevent backflows (the flow of water from a customer’s facility into public water system). In addition to these efforts, a small amount of disinfectant is added in order to prevent microorganisms from growing in the water distribution system.


You may ask, why would you need to add disinfectant when you already take these other steps to ensure the water is clean and safe? Maintaining a disinfectant residual is not free - it costs significant time, equipment, and materials, but Anaheim has concluded (as have most other public water systems) that the potential impacts of a waterborne disease outbreak are far too devastating to take the risk. We take numerous precautions to keep microorganisms out of our water system, but we know that it’s still possible they could sneak in from an unforeseen event such as a pipeline break or inadvertent backflow. Therefore, we have determined that maintaining a disinfectant residual is another prudent measure to help keep the public water supply safe.


Chlorine and Chloramine

The two common chemicals used for maintaining a disinfectant residual are liquid chlorine and chloramine. Chloramine is the combination of chlorine and ammonia and its advantages are that it will last longer in the distribution system and causes fewer disinfection byproducts (disinfection by-products are formed when chlorine reacts with naturally occurring organic matter in the water). Liquid chlorine’s advantages are: it’s safer to use, less expensive, and is more effective in killing bacteria. Because Anaheim uses groundwater which has virtually no disinfection byproduct potential and our well sites have limited space, we have decided to use chlorine. About 0.8 parts per million are added to the water at the wellhead in the form of sodium hypochlorite, a food-grade liquid bleach.


The regional water wholesaler (Metropolitan Water District of Southern California, or MWD), on the other hand, has determined that chloramine is the better disinfectant for their water system. They based their decision on the need to maintain a residual for a longer period of time (their distribution system spans six Counties in Southern California), and their surface water supplies have a high disinfection byproduct potential. They add about 2.5 parts per million at their treatment plants.


The U.S. EPA, the California Department of Public Health, and the National Sanitation Foundation have certified that chlorine and chloramine are safe for use in public water systems. However, the use of disinfectants causes disinfection by-products to form.  Water purveyors take numerous actions to ensure that regulatory limits for disinfection by-products are not exceeded.


However, while both chlorine and chloramine are great for treating water for human consumption it can be harmful to fish and could pose problems for some medical applications.  Learn more about how both chlorine and chloramine can cause problems for pet fish and people who use dialysis equipment 


Anaheim’s Water System

Some parts of Anaheim mostly receive water disinfected with chlorine while other parts may often receive water that could have chlorine and/or chloramine. Most of the west side of Anaheim receives primarily groundwater with a chlorine residual, while most of the Hills area receives a blend of MWD water with a chloramine residual and water from the Lenain Treatment Plant which contains a chlorine residual. The water from MWD is supplied though inter-connections located throughout the City that are utilized depending on water system demand and the availability of other sources of supply. In total, MWD water with a chloramine residual makes up less than 15 percent of Anaheim’s total water supply.


If you would like to learn more about water system disinfection, please feel free to contact our water quality staff via email at waterquality@anaheim.net or click on the following links.



U.S. EPA disinfectant information: 



 Updated: July 2, 2014