The Basics

    What is the Purified Water Project?

    The drought threat is real and waiting for Mother Nature is not an option. A reliable supply of safe, clean water is crucial for public health and the economy. Valley Water has been preparing for drought by investing in technology and infrastructure, including the Anderson Dam Seismic Retrofit Project, upgrading and maintaining our pipelines and water treatment plants and expanding the use of recycled and purified water.


    The Purified Water Project will allow Valley Water to develop the use of purified water to supplement existing water sources to replenish our groundwater in a manner that minimizes environmental impacts. This project will provide a drought-resilient and local water supply.   


    When completed, this project will build a facility capable of providing at least 10 million gallons per day of high-quality, drought-resilient purified water.

    What are the benefits of the project? Why is the project needed?

    Purified water produced from this project, along with existing recycled water use, will help Valley Water meet about 10% of Santa Clara County's water demand through recycled and purified water. The use of purified water for groundwater replenishment will help us diversify our water supplies especially as droughts continue to occur with increasing frequency and length due to climate change. It will also help us maintain groundwater levels and prevent overpumping of groundwater, which can cause land subsidence (sinking).

    What is groundwater recharge?

    Water that is underground, also called groundwater, is one of the county's greatest natural resources and an important part of our drinking water supply. Nearly half of the water used in Santa Clara County is pumped from groundwater basins located below the surface. The County's groundwater basins serve several important functions in that they transmit, filter, and store water. Groundwater is pumped by local water retailers, companies, and individual well owners to serve many beneficial uses, including municipal and domestic needs, agriculture, and industry. 

    Since the 1930s, Valley Water has worked to protect and augment groundwater supplies through the coordinated use of surface water and groundwater. Although groundwater is replenished naturally by rainfall and other sources, the amount of groundwater pumped far exceeds what is recharged naturally. 

    To help offset groundwater pumping and prevent over-pumping groundwater, saltwater intrusion, and land subsidence (sinking), Valley Water uses local and imported surface water to replenish groundwater through groundwater recharge facilities, including percolation ponds and creeks.

    The Purified Water Project will help supplement those groundwater recharge efforts with a locally controlled and drought-resilient water supply.

    What is purified water? How is it different from recycled water?

    Water has always been nature’s renewable resource. Purifying and recycling water simply speeds up that natural process. Recycled water generally refers to municipal wastewater that has been cleaned and meets requirements for industrial and landscape use. Purified water is highly treated municipal wastewater that has gone through additional advanced treatment and disinfection to meet and exceed state and federal drinking water standards.

    What is direct and indirect potable water reuse?

    The term potable usually refers to drinkable water.  Indirect Potable Reuse (IPR) refers to purified water that is blended with an environmental buffer such as a river, reservoir, or groundwater basin, before the water is reused. Direct Potable Reuse (DPR) water is distributed directly into a potable water supply distribution system downstream of a water treatment plant or into the source water supply immediately upstream of a water treatment plant.  


    Is purified water safe? Is it used elsewhere in the world?

    Yes, purified water is safe! The multistep advanced water purification process utilizes (1) microfiltration, (2) reverse osmosis, and (3) UV light disinfection and advanced oxidation to remove potential water contaminants. Thanks to this process, purified water meets or exceeds state and federal water drinking standards, which are verified through monitoring to ensure safety and quality. When used in groundwater replenishment, purified water also benefits from additional filtration that occurs naturally through the soil.

     With the Purified Water Project, Valley Water will join many other places in the United States and worldwide in using this water purification and groundwater replenishment method, including Monterey and Orange counties in California, the city of El Paso in Texas, Australia, and Singapore.

    To learn more about how purified water is used as a drinking water source and the purification treatment process, please visit There, you can also sign up for tours of the existing Silicon Valley Advanced Water Purification Center.

Other Project Details

    Why is another purified water treatment facility needed when we already have the Silicon Valley Advanced Water Purification Center?

    On average, the Silicon Valley Advanced Water Purification Center (SVAWPC) produces 8 million gallons per day of purified water. Much of this water is used to enhance the quality of recycled water for important industrial and landscape use. 

     With the Purified Water Project, a new facility will be built to expand Valley Water’s purified water treatment capacity to at least another 10 million gallons per day. This new drought-resilient and locally controlled water supply will supplement existing water sources used to replenish our groundwater and diversify our drinking water supply. 

     Of the two potential facility sites the project is exploring, one involves expansion at the current SVAWPC site. Valley Water is in the early stages of environmental review and securing partnership agreements for key aspects of the project. The outcome of these efforts will determine whether the SVAWPC site or the former Los Altos Treatment Plant site in Palo Alto becomes the selected site for the new facility.

    How much will the Project cost? How is it being funded?

    While the Purified Water Project is still in the early stages of planning, it is expected to cost around $600 million. The project is being developed through a potential Public-Private Partnership (P3) to assist in the design, build, finance, operation, maintenance, and delivery of the project.

    What is the Project’s schedule?

    Valley Water anticipates starting construction on the Purified Water Project in 2024. Completion of the project is expected in 2028 pending partnership agreements, permits, and environmental review.

    How much purified water will the proposed Purified Water Project produce for groundwater recharge?

    When completed, the Purified Water Project will build a facility capable of providing at least 10 million gallons per day of high-quality, drought-resilient water to help meet Valley Water’s water supply goals, which includes providing at least 10% of water demand in Santa Clara County through recycled and purified water.

    How much energy is required to purify water?

    The amount of energy required to purify water from the new proposed water purification facility will be analyzed as part of the project’s Environmental Impact Report (EIR). For reference, Valley Water’s Silicon Valley Advanced Water Purification Center (SVAWPC) uses approximately 13.2 Gigawatt hours (GWh) to produce on average 8 million gallons per day of water.  

    Most of the energy required to produce purified water is used to remove potential contaminants during the treatment process. The energy required to purify water from treated wastewater is significantly less than desalinating sea water since there is less dissolved substances and potential contaminants to remove. Below is a graph comparing total dissolved solids (TDS) between different types of water to demonstrate how much more energy it would potentially take to desalinate sea water over purifying treated wastewater. While TDS is used as an indicator for potential contaminants in water, it can also include normally occurring substances in water, like minerals and salts. The average TDS levels for tap water in our county and the maximum allowed TDS level for federal drinking water standards are also included for comparison.  

    Following the Reverse Osmosis (RO) stage of the purification process, what happens to the concentrate or brine? Does the RO concentrate harm the environment?

    As treated wastewater moves through the water purification process, impurities and contaminants are removed and concentrated into a brine. This brine is also known as RO concentrate and contains the same amount of pollutants that would have been discharged into bay originally as part of treated wastewater. The only difference is that pollutants within RO concentrate is more concentrated.

     Since 2014, the RO concentrate from the SVAWPC is blended with tertiary treated wastewater at the San José-Santa Clara Regional Wastewater Facility and discharged to the San Francisco Bay in compliance with strict environmental regulations. 

    Valley Water is working with our partners to find similar RO concentrate solutions for this new project. We are conducting the necessary rigorous evaluations and analyses of the available options for managing RO concentrate, including modeling, studies, collaborative workshops with stakeholders, assessment by an Independent Advisory Panel of Experts, and discussions with regulators. Regulators and the environmental community have been very supportive of increased water recycling and the need to manage this waste stream cost effectively. 

    How is Valley Water working with other agencies on completing this project?

    Valley Water has a history of collaboration with cities and other agencies to build and expand water reuse projects from Palo Alto to Gilroy.  Valley Water will continue to work with its partners to make potable water reuse a reality for the county.  Valley Water signed an agreement with the cities of Palo Alto and Mountain View in 2019 to support this regional purification project and is continuing to work with the cities of San José and Santa Clara to explore additional partnerships.

    Once the Environmental Impact Report (EIR) is finalized, how will modifications that arise during the planning process be addressed?

    Just like any project subject to the California Environmental Quality Act (CEQA), the EIR will examine the project as defined. If there are alterations that occur following project approval, the lead agency will review whether those changes meet the criteria set forth in CEQA as to whether additional environmental review is required. 

    Additional environmental review is typically triggered by substantial changes that have the potential to result in new or substantially more severe impacts that were not previously discussed. This additional review could take several forms depending upon the project change: an addendum, a Subsequent, or a Supplemental EIR.

The Future

    In addition to groundwater recharge (indirect potable reuse), could purified water be delivered to our water treatment plants in the future (direct potable reuse)?

    Currently, the Purified Water Project is only considering groundwater recharge (indirect potable reuse) as part of the proposed project. Direct potable reuse could be considered for a future separate project. The State Board is currently developing regulations to address direct potable reuse, but these regulations are not in place yet. Any future direct potable reuse project will need to meet these new requirements.

    Valley Water has evaluated future direct potable (drinkable) reuse opportunities, which includes supplementing raw water supplies for our water treatment plants pending state regulations. These evaluations can be found in Valley Water’s Countywide Water Reuse (CoRe) Master Plan, which is posted under the “Reports and Documents” section of the project website

    How does this project relate to the Countywide Water Reuse (CoRe) Master Plan?

    This project is consistent with the first phase of Indirect Potable Reuse in the CoRe Plan but was adjusted in terms of facility size due to new water demand projections. These projections showed lower than expected demand on our water supply as residents continue to embrace water conservation as a way of life in Santa Clara County.