Latest water quality tests show improving levels of disinfection compound

To address water quality challenges, EBMUD is adjusting operations, implementing system improvements, increasing flushing and investing in capital improvements    

East Bay Municipal Utility District officials confirm that recent water quality tests show reductions in levels of trihalomethanes (THMs), a disinfection byproduct found in chlorinated drinking water. Improvements in the organic makeup of EBMUD’s water source, Pardee reservoir, combined with corrective actions are moving the water quality needle in the right direction. EBMUD’s drinking water quality remains in full compliance with all state and federal regulations. 

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 locations 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.

EBMUD detected changes in water composition early and assembled water quality experts who recommended several actions, which were implemented by staff from across the District:

Immediate actions: 

  • Increased sampling and system flushing
  • Adjusted water treatment operations
  • Modified operations to improve source water quality
  • Installed a pilot THM removal system

Long-term capital improvements funded in the recently approved 2018-19 budget 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
  • Improvements at Orinda Water Treatment Plant


California’s historic drought, followed by record-setting rainfall,  posed challenges for drinking water systems throughout Northern California. EBMUD experienced water quality and treatment challenges due to reduced water usage, higher temperatures and higher concentrations of organic material in water from Pardee Reservoir. Disinfection byproducts including THMs are formed when chlorine reacts with organic material in water.

EBMUD’s watercontinues to meet all water quality regulations,” says Manager of Water Quality Susan Teefy. “With the recent test results showing a positive signal, EBMUD’s team of water quality staff continues to take actions to limit the formation of disinfection byproducts in drinking water. EBMUD is committed to communicating with the public on this important issue.”