Purple Pipes in Santa Clara County

The Santa Clara Valley Water District is the primary water resource agency in Santa Clara County. Water supply in the county come from different sources (fig. 1). Approximate water usage (FY 2012-13) is 323.56 MGD (million gallons per day) and the per capita water usage1 is 0.06 MG/year/resident and commuters2.

Srividya Pie Chart

Figure 1. Water Supply in Santa Clara County.

 

There has been strenuous efforts to reduce the consumption of potable water in Santa Clara County. One way is by recycling water, which is  delivered to consumers by purple pipes (fig.2).

 

Srividya Purple Pipe Pic

Figure 2: Recycled Water / Purple pipe.

 

Purple pipes supply non potable water (recycled) and are made distinguishable from fresh water (potable) pipes to avoid mixing of supplies. Purple pipes are clearly labeled “Recycled Water – Do Not Drink”. Recycled water is created from wastewater. Water used in homes and offices reaches their respective pollution control plant, where, it undergoes treatment to get converted into recycled water. The basic treatment procedures involve a primary treatment where organic and inorganic solids are removed through sedimentation and floatation; a secondary treatment where a biological conversion of extremely fine organic and inorganic solids from the primary treatment effluent is performed to remove biological oxygen demand, suspended solids and dissolved solids; a tertiary treatment is performed to further remove fine suspended solids through fine sand or other granular material. The water is finally chlorinated for disinfection. The effluent from the chlorinated tertiary treatment is used as recycled water and is transported through purple pipes by a transmission pump-system. Recycled water meets California 17 & 22 standards for drinking water and employ additional precautions to minimize contact with humans. Click here to find out more about water standards required for recycled water.  

Santa Clara County has 4 waste water treatment plants producing recycled water: Palo Alto Regional Water Quality Control Plant, Sunnyvale Water Recycling, South County Regional Wastewater Authority, and South Bay Water Recycling.

Together, they serve 2 million residents in 15 cities. In FY 2012- 13, the volume of water recycled in Santa Clara County was approximately 17.84 MGD. Recycled water contributes to around 5.5%4 of the water usage. The design capacity of each facility is illustrated in the figure 3.

 

Srividya Bar Chart

Figure 3: Design capacity of recycled water plants in Santa Clara County.

 

Recycled water in the county is being used for both commercial and residential purposes. A few notable uses include:   

·        Landscape irrigation

·        Habitat Restoration

·        Chillers, cooling towers & evaporative condensers, industrial boiler water feeds

·        Groundwater recharge

·        Other uses:  Flushing toilets and urinals, soil compaction, commercial car washes, cleaning roads, outdoor walking areas.

Some of the benefits of using recycled water include:

·         Conservation of drinking water supplies

·         Sustainable and reliable water supply, especially during drought years

·         Wastewater discharge is diverted away from the San Francisco Bay estuary

·         Preservation of saltwater marshland habitats

·         Allows continued economic growth for the region

**AF (Acre-foot/year )and HCF (Hundred Cubic Feet) can also be used for representation of volume of large scale resources. Click here for converting into appropriate units as required.

 

[1] Water use in the county refers to water that has been consumed from different sources for various end-uses. Some water supply sources include: water imported,

     ground water recharged, water from reservoirs and treatment plants.

[2] Analysis based on Annual Report of Santa Clara Valley Water District  http://www.valleywater.org/about.aspx

[3] Based on data available from http://www.valleywater.org/

[4] Assuming recycle water produced is consumed completely


Srividya Swaminathan 

July 2014

 
 
Average Rating:
0 comments: