Total Trihalomethanes Water Quality Exceedance

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

Our water system exceeded a drinking water standard in 2016. 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 (PDF) applies to East Valley Water District customers residing in the City of Highland and portions of both the City and County of San Bernardino. View a map of the District's service area here.

  1. What are TTHMs
  2. Protecting Water Quality
  3. What You Should Do

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.