Recycled and Purified Water

To ensure an adequate and reliable supply of high-quality water, Valley Water has partnered with cities and water retailers in Santa Clara County to develop recycled and purified water supplies. In calendar year 2023, about five percent of the county’s total water use consisted of recycled water, and was used primarily for landscaping, agriculture and industrial activities.

In 2021 Valley Water, in collaboration with local stakeholders, completed the Countywide Water Reuse Master Plan (CoRe Plan). This collaborative strategy integrates and expands recycled and purified water as a local, reliable, environmentally adaptive, and drought-resilient water supply. The CoRe Plan identifies and evaluates future Indirect Potable Reuse (IPR) and Direct Potable Reuse (DPR) opportunities, serving as a key component of the region's Water Supply Master Plan.

On February 27, 2024, the Valley Water Board approved moving forward with both a demonstration and a full-scale direct potable reuse project. This strategic shift from a smaller Indirect Potable Reuse (IPR) project to a larger-scale DPR initiative was made possible by the recent adoption of DPR regulations on October 1, 2024. Currently, Valley Water is actively working to develop a locally controlled and drought-resilient supply of purified water through the Purified Water Project.

• View the Countywide Water Reuse Master Plan (CoRe Plan)

There are four individual Recycled Water Systems (RWS) providing service in Santa Clara County. These systems receive recycled water from a single Producer (City of Sunnyvale, Palo Alto Regional Water Quality Control Plant (RWQCP), South Bay Water Recycling (SBWR), and South County Regional Wastewater Authority(SCRWA)).

Additional information pertaining to each of these systems:

City of Sunnyvale - RWS

• City of Sunnyvale

RWQCP - RWS

• City of Palo Alto

SBWR

• South Bay Water Recycling – Final Report 2015
• South Bay Water Recycling – Final Report 2015 Appendices
• South Bay Water Recycling  

South County RWS

• 2015 South County Recycled Water Master Plan Update

Water has naturally been recycled through the earth’s water cycle for millions of years. During the past 200 or so years, what has been termed “unplanned recycling” has occurred. This consists of upstream cities discharging their treated wastewater to a river or other waterway from which downstream cities obtain water for treatment to drinking water standards. For example, the Sacramento River receives treated wastewater and serves as a water source for many towns and cities.

Recycled water is wastewater that is cleaned through multiple levels of treatment. It is clean and safe for non-potable uses such as irrigation, cooling towers, golf courses, and agriculture. Recycled water is treated to strict standards set by the Division of Drinking Water and is rigorously monitored by local, state, and federal agencies to ensure it continuously meets those standards.

All recycled water in Santa Clara County meets or exceeds standards set by the state for the various uses of recycled water.

Benefits of recycled water:

• Conserves drinking water supplies.
• Provides a dependable, drought-proof, all-weather, and locally-controlled water supply.
• Helps restore and preserve our saltwater and tidal habitats by reducing freshwater discharge to the Bay.
• Is more economical and environmentally sustainable because it is less energy-intensive and has a lower carbon footprint than many other water supply sources

Water has always been nature’s renewable resource and is constantly moving through the water cycle. Purifying water simply speeds up that natural process by using a multistep effort to remove potential water contaminants, creating a drought-resilient and sustainable water source. Purified water first starts out as highly treated wastewater that has already gone through a multi-step treatment process at a wastewater facility. Once that highly treated wastewater arrives at the Silicon Valley Advance Water Purification Center, it goes through a multi-step purification process, which can include micro-filtration, reverse osmosis, UV light disinfection, and advanced oxidation. This purified water is treated to strict standards set by the Division of Drinking Water and is rigorously monitored by local, state, and federal agencies to ensure it continuously meets those standards. All purified water in Santa Clara County meets or exceeds standards set by the state.

How Safe is Purified Water?
As mentioned, purified water is safe and meets or exceeds state and federal drinking water standards. It is tested regularly by our certified Water Quality Lab to ensure safety and quality. Upon completion of the Purified Water Project, Valley Water will be able to expand its drinking water supply by integrating purified water with Santa Clara County’s existing drinking water resources. Valley Water will join many other places in the United States and worldwide in using this advanced water purification process including Monterey and Orange counties in California, Big Spring and El Paso in Texas, Australia, and Singapore.

The Silicon Valley Advanced Water Purification Center (SVAWPC) and the Purified Water Project
To learn more about how purified water is used as a drinking water source and the purification treatment process, please visit purewater4u.org. There, you can also sign up for tours of the existing SVAWPC, which currently produces up to eight million gallons per day of highly purified water.

This highly purified water is blended into existing recycled water provided by SBWR, which improves overall recycled water quality so that the water can be used for a wider variety of irrigation and industrial purposes.

For more information about this effort, please visit the Purified Water Project website.

Reverse Osmosis (RO) is a key component of the DPR treatment process. A significant challenge for this process is developing a safe and effective strategy for the disposal of reverse osmosis concentrate (ROC), the byproduct of RO purification. ROC contains the same contaminants as typical treated wastewater but at a much higher concentration (approximately six times greater). Due to this high concentration, directly discharging ROC through existing effluent outfalls without additional treatment poses regulatory and environmental challenges, particularly in the Lower South Bay, where mixing and dilution are limited.

Conventional ROC treatment methods are often expensive and energy-intensive, which has led to an increasing interest in nature-based solutions (NBS) as a more sustainable and multi-benefit alternative for ROC treatment.

Valley Water has been actively investigating NBS as a sustainable approach to managing ROC. NBS utilizes natural processes to reduce contaminants while also providing co-benefits such as habitat creation and flood protection and consequently assist with meeting the regulatory requirements and protecting the health of San Francisco Bay. Valley Water is actively exploring NBS as a viable, eco-friendly approach for managing ROC.

Valley Water has been undertaking pilot studies to evaluate the feasibility of different types of NBS to identify the most efficient and cost-effective option (or combination of options). These pilot projects include:

• Open-Water Treatment Cells
• Horizontal Levees
• Floating Wetlands

Open Water Treatment Cells

Open water treatment cells use natural processes, such as sunlight and the activity of bacteria and algae, to break down contaminants. These shallow cells allow sunlight to penetrate, helping to reduce pollutants such as nitrates and some organic compounds.

A pilot study at SVAWPC from 2017–2019 integrated ozonation before the cells to improve efficiency. Results showed the cells removed 28% to 47% of nitrates, especially in summer when sunlight is more intense, and reduced some pharmaceuticals and organic compounds. However, metals like copper and nickel were harder to treat, and pesticide removal was limited. Potential improvements could include extending the residence time of ROC in the cells or enhancing pre-treatment with advanced oxidation processes like ozonation. While open water treatment cells present a sustainable solution with potential co-benefits, their efficiency can vary with seasonal changes, and they require substantial land areas for implementation.

Floating Wetlands

Floating wetlands are an engineered natural treatment system where water flows through the roots of hyperaccumulating plant species growing on floating platforms. These roots support provide high surface area for biofilms that adsorb and extract contaminants. These biofilms enhance nutrient uptake and facilitate the breakdown of contaminants through natural processes.

Valley Water has been testing floating wetlands at SVAWPC, showing promising results in reducing nitrogen and copper, especially in warmer months when biological activity increases. However, they were less effective at removing contaminants like nickel and phosphorus and faced challenges with high salinity levels in the ROC. Further improvements in design and plant selection could enhance their performance. When land is available, floating wetlands provide an eco-friendly way to treat ROC while offering added benefits to the community.

Horizontal Levees

Horizontal levees are subsurface flow wetlands designed to provide flood protection, habitat restoration, and water treatment. These levees are constructed with a gradual slope filled with layers of gravel, sand, and woodchips, which filter the water as it flows through, leveraging microbial processes to break down contaminants.  

In 2020, Valley Water joined the horizontal levee pilot project at Oro Loma Sanitary District (OLSD) in partnership with UC Berkeley, East Bay Dischargers Authority, and San Francisco Estuary Institute. ROC from the SVAWPC was transported to OLSD at a rate of 10,000 gallons/week and then fed to horizontal levee cells to evaluate the removal of nutrients and metals.

Phase 1 of this project was completed in 2022 and yielded encouraging results indicating that cells receiving ROC exhibit removal of nutrients, trace organic contaminants, copper, and showed improvement of general water quality parameters. However, the removal efficiency for certain trace organic contaminants was lower, likely due to differences in redox conditions.

 To enhance overall performance, adjustments such as optimizing the slope, substrate composition, and redox conditions have been considered for Phase 2,  of this project particularly for improving the removal of persistent metals and organic pollutants.

Phase 2, launched in 2022, aims to improve treatment efficiency by enhancing cell design and addressing emerging contaminants like PFAS using advanced materials like geo-media and activated carbon. Beyond water treatment, horizontal levees help protect against storm surges and sea-level rise, supporting Valley Water’s commitment to sustainable, eco-friendly infrastructure.