Disinfection byproducts

EBMUD drinking water quality remains in full compliance with all state and federal regulations. 

Our treatment and distribution systems are regulated by the United States Environmental Protection Agency and the State of California Division of Drinking Water, under the state and federal Safe Drinking Water Acts. Municipal water agencies that use surface water protect public health by filtering and disinfecting all water delivered to our customers. These processes reduce viruses, Cryptosporidium, E. coli, Giardia, and other water-borne pathogens that can cause illnesses.

Filtration: Coagulants are added, and then the water passes through filters of anthracite and sand to remove particles like dirt, parasites, bacteria, and viruses.
Disinfection: A disinfectant (chlorine) is added to kill any remaining parasites, bacteria, and viruses, and to protect the water from germs when it is piped to homes and businesses. Disinfectants are added before filtration and/or after, depending on the water treatment plant.
Corrosion Control: After filtration and disinfection, the water chemistry is adjusted to minimize corrosion, particularly of metal pipes and plumbing components.

When chlorine is used for disinfection, disinfection byproducts such as trihalomethanes (THMs) will form. Naturally-occurring organic matter in the water reacts with chlorine to form THMs. THMs are present to some degree in all chlorinated drinking water systems and are regulated so they don’t approach levels that may present a risk to public health. 

Natural organic matter in water originates from leaves, grass, and other plant material that gets washed into the reservoirs. As the seasons change, the amount of organic matter in the water changes, and therefore the amount of THMs that form when the water is chlorinated also varies seasonally.

EBMUD has begun work on several large capital projects at our treatment plants and in our reservoirs that will help us better control formation of disinfection byproducts. These projects will allow us to use less chlorine, remove some of the natural organic matter, more precisely adjust the water chemistry to control disinfection byproduct formation while simultaneously disinfecting the water.  

Trihalomethanes, or THMs, are byproducts of the process used to disinfect water during the treatment process. They are formed when natural organic material, such as the decaying vegetation commonly found in lakes and reservoirs, reacts with chlorine used to treat the water.

Yes. THMs are found to varying degrees in all chlorinated drinking water. They form when chlorine reacts with naturally-occurring organic matter in water. Chlorine is necessary for disinfection and required by regulations to protect public health. It has been used to disinfect water for almost a century due to its effectiveness at killing bacteria and viruses in water, reducing the incidence of intestinal illness and other health problems caused by waterborne pathogens.

Yes, the water is safe to drink. EBMUD drinking water quality continues to meet or surpass every state and federal public health requirement. The EPA has set regulatory limits on THM concentrations to be protective of public health for all potential health risks. EBMUD drinking water is below the regulatory limits.

If you have a specific medical condition that you are concerned about, please consult your doctor for recommendations.

As the climate changes, major changes to treatment processes may be required to deal with changes resulting from reduced water consumption, higher temperatures, and higher concentrations of natural organic carbon in raw water. These changes are significant, and would require a major investment by EBMUD. The large construction project underway at the Orinda water treatment plant, which includes adding ultraviolet light for disinfection and a new chlorine contact chamber, is one example.

California’s historic drought, followed by record-setting rainfall, continues to have impacts on drinking water systems throughout the San Francisco Bay Area. The East Bay Municipal Utility District experiences water quality and treatment challenges due to reduced water consumption, higher temperatures, and higher concentrations of natural organic carbon in our untreated ‘raw’ water from Pardee Reservoir in the Sierra foothills.

Reduced water consumption – a tremendous benefit for EBMUD’s water supplies and future water needs – has reduced flows and water use in our distribution systems. Reduced use can result in increased water age – the amount of time water remains in our pipes and storage tanks.

Water age, along with water chemistry changes, affects the residual disinfectant used to protect the distribution system and the amount of disifnection byproducts that form. Other factors like the pH and temperature of the water also impact disinfectant byproduct formation. 

EBMUD tests for THMs as part of routine testing in our distribution system throughout the year. Samples are taken from 16 different locations each quarter. Individual numbers can vary widely due to many factors. 

We regularly report these levels to the State Water Resources Control Board Division of Drinking Water, as well as in our Annual Water Quality Report (AWQR) available to the public.

Studies show that some people with long-term exposure to drinking water containing THMs in excess of state and federal limits may have an increased risk of getting cancer. This is not the case with EBMUD drinking water, which continues to meet all state and federal guidelines. 

Yes, it is safe to shower to bathe, and wash dishes.

Pregnant women may wish to consult their physician for advice and drink water according to their doctor's recommendations. 

Planned capital improvements to make water treatment plants more resilient to changes in source water quality include:

  •  Improved removal of organic material at the Walnut Creek and Orinda water treatment plants 
  •  A project to improve water quality in San Pablo Reservoir
  •  Disinfection improvements at Orinda Water Treatment Plant

These are some of the significant investments EBMUD is making to ensure we continue to provide reliable, high quality water to our customers.

EBMUD meets or surpasses all state and federal drinking water requirements and thus water purification filters are unnecessary. However, there are filters that remove THMs. If you choose to filter your water, make sure you purchase a device that has been tested and certified, and follow manufacturer guidelines for filter replacement to avoid creating additional water quality problems.

Frequently asked questions in Spanish and Chinese

Additional resources 

Questions on tap water quality: