Frequently Asked Questions


What is recycled water?

Recycled water is wastewater that has been purified through a high level of treatment.  This processed water is treated to strict standards set by the California Department of Health Services and is constantly monitored by local, state, and federal regulatory agencies to ensure it continuously meets those standards. 

Recycled water has been found safe for irrigation, industrial and agricultural uses.  In fact, all water on Earth is in some way recycled.  Mother Nature has been recycling water and wastewater for millions of years through a natural cleansing process of sedimentation, organic consumption, natural filtration and disinfection. Modern wastewater treatment technology essentially speeds up this natural process.

Is recycled water safe?



Is recycled water safe for irrigating gardens and landscaping?

Yes, the State has approved this type of highly treated "tertiary" recycled water for use on all types of landscaping, turf, gardens and crops. Recycled water is not for drinking, however.  To be completely safe, and avoid human ingestion, it should not to be sprayed on people or left in ponds that children could play in. 


Is it safe for children and pets to play on grass irrigated by recycled water?

Yes, The California Department of Health Services has very high treatment standards for recycled water.  Palo Alto’s recycled water meets or exceeds all state standards for water used for irrigation and other uses with similar public exposure.  Ponding of recycled water on grass or other areas is specifically prohibited as added insurance that a significant amount could not be ingested by children.  In addition, according to Dr. Stanley Deresinski, Clinical Professor, Stanford School of Medicine, one would have to drink at least 12 gallons of reclaimed water, in a single sitting, in order to ingest an infectious dose of coliform bacteria. 


What about contaminants that are not removed from the water?

While small concentrations of pollutants are found in recycled water, there is no exposure route for these compounds to be ingested by humans when using recycled water for landscape and industrial purposes.  Program staff monitor research regarding treatment technologies, mechanisms of human exposure, and health risk assessments to ensure that reuse practices protect human health.        


Is the use of recycled water for irrigation regulated by government?  

Yes.  The California Department of Public Health (DPH) creates and enforces the rules for recycled water usage.  California laws regulating recycled water are located in the Health and Safety Code, the Water Code, and Titles 17 and 22 of the California Code of Regulations.  A permit process, training, signage and a number of restrictions apply to entities transporting and applying recycled water from the RWQCP.  In Palo Alto, water haulers must complete a permit process, training, and abide by a number of regulations for the transport of water from the RWQCP.  Residents or businesses accepting the recycled water must read and sign a statement to insure they are fully aware of the recycled water application and its restrictions.     


Is recycled water being used now?

In the Palo Alto area, recycled water is used for irrigation of parks and golf courses and habitat restoration.  Recycled water is used for landscape irrigation at Palo Alto Golf Course, Greer Park, Shoreline Golf Course and many businesses in Mountain View.  Palo Alto’s Emily Renzel Marsh is a freshwater marsh fed with recycled water.  Recycled water is also being used in thousands of locations nationwide and worldwide.   


Is recycled water used elsewhere?  

Recycled water is used in thousands of locations nationwide. More than 170 billion gallons of water are recycled in California each year.


How is recycled water treated?

Wastewater from homes and businesses in East Palo Alto, Los Altos, Los Altos Hills, Mountain View and Palo Alto is piped through sanitary sewers to the Regional Water Quality Control Plant where it undergoes primary, secondary, and advanced stages of treatment.  For more information on the treatment process, please refer to the treatment process.


What is "tertiary" recycled water?

Tertiary recycled water is the highest quality recycled water.  It undergoes an extra process of UV exposure and chlorine treatment.  It is acceptable for human contact, but not suitable for drinking, swimming, or bathing.


Are recycled water supplies kept separate from drinking water? 

Yes.  Standard practice requires separate pipes for drinking water and recycled water.  Guidelines set by the Department of Health Services ensure that recycled water facilities are clearly distinguishable from other water facilities to avoid mixing of supplies.  Pipes are colored purple, and labeled with the words "Recycled Water– Do Not Drink."


Is recycled water the same as gray water? 

No.  Gray water is water from clothes washing machines, or similar water which, although untreated, is not contaminated by human waste or food preparation.  Recycled water is cleaner, safer, and has far less restrictions on its use than gray water.


Are there problems with the salt content of the RWQCP recycled water?

Palo Alto’s recycled water has been used on almost all plants and grasses successfully for many years.  However, it is saltier than the drinking water supply.  It is not recommended for Redwood trees or other salt sensitive plant species.  Salt sensitive plants commonly found in the Palo Alto area include, azalea, rhododendron, camellia, citrus trees, redwood trees, and to a lesser extent, roses.  Most of these salt sensitive plants are "acid-loving," meaning that they prefer moist well-drained soil with a pH between 4.5 - 6.0.  Although recycled water is generally considered safe for most types of landscape plants, Purple Pipe Water Services takes special care around salt sensitive species.  To minimize damage, we divert recycled water away from the foliage and roots of these plants.  Palo Alto and other nearby cities have already completed projects that have substantially reduced salt levels (as measured by total dissolved solids or “TDS”), and will continue to plan and implement projects that will further reduce TDS levels.  Chapter 2 of the Draft Environmental Impact Report for Palo Alto Recycled Water Project describes these efforts.  

For detailed information regarding TDS (total dissolved solids)/salinity, please see pages 105-109 of the City of Palo Alto Recycled Water Project - Draft Environmental Impact Report at:

Note:  If your property has lots of salt sensitive plants, you may prefer to have construction groundwater delivered instead.  Construction groundwater has a lower salt content, but is not filtered or purified.  The groundwater doesn't come with a chemical analysis since it will be different at each construction site and may have suspended solids.  Extra service fees may apply.


Why is recycling water important? 

By recycling water, residents and businesses can continue to irrigate landscaping, even during severe droughts.  Every gallon of recycled water used on landscaping means a gallon of potable water is saved for drinking and other uses.  Limited water supplies will continue tightening statewide.  The Santa Clara Valley Water District estimates that by the year 2020, the South Bay could experience severe water shortages during a drought unless efforts are made to increase water supplies.