Total Trihalomethanes Water Quality Exceedance

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East Valley Water District has Levels of Total Trihalomethanes (TTHM) Above the Drinking Water Standard


Our water system recently exceeded a drinking water standard. Although this is not an emergency, as our customers, you have a right to know what you should do, what happened, and what we are doing to correct this situation.

We routinely monitor for the presence of drinking water contaminants. Water sample results from April 14, 2016 to February 24, 2017 showed the annual average of Total Trihalomethanes levels at three locations of 92 parts per billion (ppb), 87 ppb and 84 ppb. This is above the standard, or maximum contaminant level (MCL), of 80 ppb. 

There is no additional action necessary on your part.

This public notice applies to East Valley Water District customers residing in the City of Highland and portions of both the City and County of San Bernardino. For a map of the District’s service area click here.

What are TTHMs?


TTHMs are a group of four chemicals that are formed during the water treatment process when chlorine reacts with organic materials such as leaves, plants and soil in the untreated water. Chlorine is the most common disinfectant used to eliminate disease causing pathogens (i.e. bacteria and viruses). A rise in TTHMs can result from increased chlorination during the treatment process, high organics in source water, drought conditions, or limited water circulation within the pipeline system. Water agencies throughout California have seen increases in organics where seasonal conditions boosted the annual average, which is the measurement for this water quality element. 

Taking Action to Protect Water Quality


  • We are working with the State Water Resources Control Board– Division of Drinking Water to evaluate the water supply and researching options to correct the problem. These options may include treating the water to remove TTHM or adjusting the District’s water supply.
  • Because compliance is measured based on an average, the District anticipates returning to compliance by late 2017.
  • However, current water samples show that the water provided today meets state and federal standards. 
  • We anticipate having permanent solutions to this problem by April 2019, which include several infrastructure projects. In the meantime, staff is making a number of adjustments to continue water quality for our community, for example:
    • Increased water quality sampling
    • Increasing system water circulation to prevent stagnation
    • Adjusting the water supply used in response to the water quality sampling results
    • Evaluating new treatment processes
    • Strategic fire hydrant flushing

What Should You Do


  • You do not need to use an alternative water supply (e.g., bottled water). The water provided at your tap is safe for drinking.
  • This is not an immediate risk. If it had been, you would have been notified immediately. However, drinking water containing these by-products in excess of the MCL over an extended period of time may lead to liver or kidney problems, or nervous system effects, and may lead to an increased risk of cancer.
  • If you have other health issues concerning the consumption of this water, you may wish to consult your medical doctor.
  • Please share this information with all the other people who drink this water, especially those who may not have received this notice directly (for example, people in apartments, nursing homes, schools, and businesses). You can do this by posting this public notice in a public place or distributing copies by hand or mail. Other community members include:
    • Schools: Must notify school employees, students and parents (if the students are minors).
    • Residential Rental Property Owners or Managers (including nursing homes and care facilities): Must notify tenants.
    • Business Property Owners, Managers or Operators: Must notify employees of businesses located on the property.
    • Medical Professionals: East Valley Water District has notified Loma Linda University Medical Center, Beaver Medical Group, St. Bernardine Medical Center Dignity Health, and Kaiser Permanente. If your medical doctor does not belong to one of these providers, please give them a copy of this notification.