Disinfection byproducts

EBMUD takes steps to stem formation of disinfection byproducts, maintain high quality drinking water.

This information is available below in Spanish and Chinese.

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.

EBMUD drinking water quality remains in full compliance with all state and federal regulations. To ensure continued compliance, the District has been taking action over the last several months to address elevated levels of disinfection byproducts. 

Municipal water agencies like EBMUD protect public health through a two-step process to filter and disinfect all water we deliver. These processes remove Cryptosporidium, E. coli, Giardia intestinalis, and other water-borne pathogens that can cause illnesses such as diarrhea, cholera and Hepatitis A.

Filtration: Water passes through filters of sand, gravel, and charcoal with various pore sizes, to remove dissolved particles, like dust, parasites, bacteria, viruses, and chemicals.
Disinfection: A disinfectant (chlorine or chloramine) 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 can be added before filtration and/or after, depending on the water treatment plant).

Over the past few years, in our regular collection and analysis of water samples throughout the distribution system, the District began to see a rise in the concentration of trihalomethanes (THMs) – a disinfection byproduct formed when chlorine reacts with naturally-occurring organic matter in water.

THMs are present in all public drinking water systems and are regulated so they don’t approach levels that may present a risk to public health. Those concentrations don’t exceed state and federal standards, but they are above EBMUD’s internal water quality goals. This prompted EBMUD to take action.

The increase in THMs can be attributed to more natural organic matter and sediment in EBMUD’s water supply. To address this challenge, months ago, EBMUD increased water quality sampling, implemented operational changes and, this June, a new flushing program. These immediate steps are in addition to long-term infrastructure upgrades already underway.

EBMUD confirms that recently water quality tests show reductions in levels of THMs. Improvements in the organic makeup of EBMUD's source water, Pardee Reservoir, combined with corrective actions are moving the water quality needle in the right direction. 
Tests conducted throughout EBMUD service area in July 2017 show THM concentrations well below the Maximum Contaminant Level (MCL) of 80 parts per billion.

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 formed when chlorine reacts with naturally-occurring organic matter in water. Current levels in EBMUD water are higher than they have been previously; however THM concentrations do not exceed state and federal public health requirements. To ensure continued compliance, EBMUD has been taking corrective action over the past several months to stem rising levels of disinfection by-products.

Chlorine is necessary for disinfection and required by regulations to protect public water supplies. 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 germs.

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.

Recent water quality tests show reductions in levels of trihalomethanes (THMs), a disinfection byproduct found in all drinking water. Tests conducted at 16 locations throughout EBMUD’s service area in late July 2017 showed THM concentrations ranging from 30 parts per billion (ppb) to 57 ppb. All sites are well below the Maximum Contaminant Level (MCL) of 80 ppb. The MCL was developed to limit long-term exposure to THMs while balancing the need to disinfect water to protect the public from disease-causing pathogens. 

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.

To address this challenge, the District has increased water quality sampling, implemented operational changes and a new flushing program. EBMUD is testing THM removal technologies through a pilot aeration system at the Lafayette Water Treatment Plant. In addition, infrastructure upgrades designed to lower THMs are already underway.

The District is currently flushing pipes in areas most affected by these conditions. Flushing removes sediment and mineral deposits, and helps maintain a chlorine residual within the distribution system to ensure the delivery of high quality water to customers. Customers in Orinda and Berkeley have been notified via Nextdoor about flushing in their neighborhoods.

This past November, EBMUD configured a pilot water treatment facility to test new treatment processes, doses and configurations. EBMUD is using this testing facility to evaluate different coagulants and filter configurations to address these water quality challenges.

EBMUD is also considering accelerating plans that are already underway, including pretreatment and disinfection modifications at our in-line water treatment plants. Our five-year capital improvement plans include reliability and improvement projects at several inline water treatment plants, which will reduce disinfection byproducts significantly.

Ultimately, major changes to treatment processes may be required to deal with changes due to 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.

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 is experiencing 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, can affect the residual disinfection used to protect the distribution system – the treatment that removes water borne pathogens from our drinking water. Flushing moves water through the distribution system, removes sediment and mineral deposits that can accumulate in water pipes, and helps maintain our high water quality throughout the drinking water system.

EBMUD tests for THMs as part of routine testing to monitor treated water. We have observed that levels have increased over the past two years. System average is currently at 58 parts per billion (ppb), exceeding our own internal goal of 40 ppb, but continues to be under the state and federal limit of 80 ppb.

We regularly report these levels to the State Water Resources Control Board Division of Drinking Water, as well as report quarterly on water quality to our Board of Directors. We publish results in our Annual Water Quality Report (AWQR) available to the public and notify our customers (via postcard and bill insert) when the AWQR is published.

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. 

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.

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

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

Frequently asked questions in Spanish and Chinese

Additional resources 

Questions on tap water quality: