Understanding Recycled Water

Updates

11/21/22 – Statement from The City of Redwood City

The City of Redwood City distributes recycled water that meets the Title 22 California Code of Regulations established by the State Water Resources Control Board – Division of Drinking Water (DDW). Our recycled water, produced at the Silicon Valley Clean Water treatment plant, is wastewater that has been treated to the highest classification of recycled water defined by DDW as Disinfected Tertiary recycled water. It undergoes intensive sedimentation, biological treatment, and filtration and disinfection processes. Furthermore, the water is extensively monitored, tested, and reported on by Silicon Valley Clean Water and the City.

Recycled water has a number of uses that have been approved by DDW, such as toilet flushing, landscape irrigation, water features, construction purposes, and other industrial applications. However, recycled water is not approved for drinking. As such, the City works closely with recycled water customers to ensure that a customer’s recycled water system is designed, constructed, operated and maintained for safe use. The odor and discoloration from recycled water generally correlates with water age in the distribution system, which is common and expected.  The water age in the system is the highest when the demands in the system are the lowest; generally, around this time when irrigation needs are low.

There are several sites in Redwood City, including the Stanford Campus, that are employing recycled water for State-approved non-drinking purposes to help conserve our precious drinking water resource. In light of potential droughts and water restrictions in California, these water conservation efforts to safely utilize recycled water will significantly reduce the demands on our drinking water supply. For more information regarding recycled water, please visit our FAQ page here.

Background Information

Water reuse (also known as water recycling) reclaims water from a variety of sources, treats it, then reuses it for purposes like irrigation, landscaping, toilet flushing, groundwater replenishment, industrial processes, and environmental restoration.  San Francisco Public Utilities Commission (SFPUC) provides treated water from the Hetch Hetchy and other local reservoirs of surface water; giving an additional benefit of recycled water to discharge less treated wastewater into the bay.

Redwood City initiated their recycled water system development program in 2005 to create a drought-proof water supply that reduces demands on pristine portable water in various parts of the city.  In 2019, Redwood City expanded their recycled water system to include the Stanford in Redwood City extension project.  The purple water pipes that you see throughout areas of the city and around the Stanford Redwood City campus indicate the recycled water system.  

The Stanford Redwood City campus uses recycled water for irrigation and building meters that supply reclaimed water to our restroom toilets and urinals.  All of the buildings, except Cardinal Hall, use reclaimed water.  None of our sinks or showers rely on the recycled water system.

Treated wastewater, in many cases, still has nutrients such as ammonia and nitrogen (which also causes odor).  The odor and discoloration from the recycled water generally correlates with water age in the distribution system, which is expected.  The water age in the system is the highest when the demands in the system are the lowest; generally, cooler times of the year when irrigation needs are low.  In addition, the Stanford recycled water main pipeline extension is currently only serving the SRWC campus.  Since there is a dead end in the recycled water main pipeline, there is a lack of recycled water flow at the end of the recycled water main pipeline, resulting in increased recycled water age.  

To remedy the issues above, the City of Redwood City will actively perform periodic operational flushing to ensure the movement of water in pipelines. They also plan to boost chlorination to increase the chlorine residual in the system. Through these water management practices, the City ensures to provide the best recycled water quality to Stanford.

The flushing process returns water for further treatment and is not flushed down the drain.  660 gallons of reclaimed water is discharged into a water tank trailer, then transported to the Redwood Shores water plant for re-use.  Operational flushing is conducted at the recycled water hydrant, located near the corner of Broadway Street and 2nd Avenue.

Resources:

Redwood City’s Recycled Water:
https://www.redwoodcity.org/departments/public-works/water/recycled-water

Water Reuse from the United States Environmental protection Agency (EPA): 
https://www.epa.gov/waterreuse/basic-information-about-water-reuse