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Water Main Flushing "Scouring" water mains helps maintain water quality and protect public health
To flush a water main, selected hydrants along a section of the main are opened. The high velocity of the released water scours, or “flushes” the main, removing any collected sediment. The water is released onto the street, the chloramine is removed by dechlorination tablets, and the water enters the storm drain run-off system. Flushing takes about 15 minutes for each hydrant. In the past, MMWD performed flushing at night to minimize the impact on residents. In 2011 MMWD began flushing mains during the day to save the overtime costs of sending crews out at night. During flushing, customers may notice water in the street as it enters the storm drain system. To conserve water, MMWD performs unidirectional flushing of the water mains, which uses significantly less water than conventional flushing. We achieve this by isolating flush runs, which increases water velocity. In addition to water in the street, during flushing customers may notice changes in their own plumbing, including slight pressure drops, air in the pipes or “dirty” water. To counter these effects, we recommend restricting water use (especially of hot water) during flushing and running the cold water for a short time afterward to remove any loosened sediment in the pipeline. Be assured the discoloration is not a health concern and is comprised predominantly of rust. 2013 Water Main Flushing Schedule This year MMWD will be flushing water mains in Fairfax, San Anselmo, Ross and the San Geronimo Valley. Flushing will occur on Wednesdays between approximately 8:00 a.m. and 2:30 p.m.
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As recommended by the California Department of Public Health, MMWD “flushes” approximately 20 percent of its water mains each year to remove sediment buildup in transmission and distribution pipelines because this buildup can impair water quality. Sediment buildup can be particularly high in areas with dead-end pipes and in neighborhoods with older cast iron mains, and MMWD wants to ensure customers in these areas are also delivered high quality water.
