If you see large quantities of water running down the street in Mill Valley, Marin City or Sausalito in the coming weeks, it is probably no cause for alarm: The Marin Municipal Water District’s annual water main flushing program is currently underway in southern Marin. Water main flushing is recommended by the California Department of Health Services to help maintain water quality by removing sediment buildup in transmission and distribution pipelines.
Each year MMWD “flushes” approximately 20 percent of its water mains. To flush a water main, selected hydrants along a section of the main are opened. The high velocity of the released water scours the main, removing any collected sediment. The water is released onto the street, the chlorine 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. Last year the district began flushing the pipes during the day to save the overtime costs of sending crews out at night. This year the district will again be flushing the mains in the daytime to reduce costs without compromising water quality.
During periods of flushing, customers may notice large quantities of water in the street, as well as slight pressure drops, air in the lines or “dirty” water in their own plumbing. If you notice these effects, we recommend running cold water through an outdoor tap or garden hose for a short time to remove any loosened sediment in the pipeline. This water can be safely used on plants.
Flushing began January 12 in Mill Valley and is scheduled to continue most Thursdays through March 22 in Mill Valley, Marin City and Sausalito. Click here for a complete schedule.