Frequently Asked Questions

Frequently Asked Questions About Advanced Water Purification

To help provide a solid foundation for solutions that can help sustain our natural resources, water reuse and desalination facts and terminology have been provided. By understanding the facts and the terminology along with the existing misconceptions, one can begin to understand the needs and benefits of
water reuse and desalination.

Can Santa Clara County exist on its current water supply?

No. The Santa Clara Valley Water District imports 55% of its water from the Sierra snowpack. The rising cost of imported water, recurring drought, climate change and population growth means that the need for a local water supply is crucial to Santa Clara County’s future water needs.

Can’t we just conserve more water and not have to drink purified water?

The water district has aggressive plans to conserve more water; however, conservation alone is not enough to meet our current future water needs. Purified water is a reliable and locally controlled water supply that meets and exceeds all California primary and secondary drinking water standards. Purified water not only helps protect the region’s groundwater supplies but, more importantly, it can help us ensure that we can sustain our thriving economy and way of life.

During the most recent drought, was there an additional cost to the District to import more water?

Yes. The law of supply and demand affects imported water prices. Available imported water for the District can drop to as low as 5% (or less) for normal supplies from the State Water Project. The District then must pay high on-the-spot market prices to make up the difference.

What is the cost of purified water per gallon?

The normalized production cost of water from the SVAWPC is less than a penny ($.005) per gallon.

What is the cost comparison between operating a seawater desalination plant, Silicon Valley Advanced Water Purification Center and imported water?

The cost of imported water varies during years of drought and allocation from the State Water Board. The vulnerability of imported water to drought and environmental regulation has been repeatedly shown, which is why purified is a safe and reliable source for our future water supply. On an annual basis, the purification center costs $3.6-$5.5 million to operate and produce 8 million gallons of purified water per day (MGD). A desalination plant, which purifies seawater to produce drinking water, can cost anywhere from $11.2- $17.6 million dollars per year to operate and produce 8 MGD. In terms of energy usage, the pressure needed to run the reverse osmosis feed pumps is 190 pounds per square inch when purifying reused water. Desalination requires the pressure to be increased to 900-5,000 pounds per square inch, which significantly increases the energy usage and costs.

How much would expansion of purified water cost in Santa Clara County?

The district is still in the very early planning process for potable reuse and does not know yet the full costs. It is important to keep in mind that an expansion project like this will include expansion of the purification facility from 8 MGD to 32 MGD, building new pipelines to transport the water to groundwater basins, and associated infrastructure. Overall, the current cost estimate for this program, which includes the five different construction projects, is estimated to cost $1 billion.

Are there other water agencies exploring purified water as an alternative drinking water source?

This multi-barrier water purification process is currently already in operation at water districts in the state, nation, and globally. For example, Orange County Water District in Southern California is one of several water agencies in California that has implemented potable reuse programs. The Orange County project produces 100 MGD of purified water used to replenish groundwater basins there. Water purification is also used in Virginia, Texas, Colorado, Singapore, Australia and more.

How is the purified water being used right now, and how will it be used in the future?

The highly purified water is currently blended with the recycled water produced at the San Jose-Santa Clara Regional Wastewater Facility, to enhance the quality and expand the usage of recycled water for irrigation and industrial purposes. In the future, the water district plans to augment our drinking water supplies by using purified water to replenish groundwater basins.

Why do we need to expand the use of recycled water?

The Santa Clara Valley needs additional supplies to fill projected future water supply shortfalls. Highly purified recycled water is one new, locally developed and reliable water supply. Provided through proven technologies, it is a drought-proof water supply that can help ensure the valley has safe sustainable water now and into the future. By using water that would typically be released into the San Francisco Bay, we also benefit from local resource. Freshwater discharge to the Bay can also impact sensitive salt marsh habitat. Recycled water is a locally controlled source, unlike imported water.

What specific steps is the water district taking to expand recycled water use?

The Santa Clara Valley Water District has partnered with the cities of San José and Santa Clara to build the Silicon Valley Advanced Water Purification Center, a state-of-the-art facility to help meet Santa Clara County’s future water needs. The $72 million purification center in San José produces up to 8 million gallons of highly purified water per day, making it the largest advanced water purification plant in Northern California.

Are pharmaceuticals and personal care products removed in the water purification process?

Yes. The highly purified water produced is safe, clean and constantly monitored at every step. Results show that reverse osmosis and advanced oxidation processes are effective at removing pharmaceuticals and personal care products. All results showed the levels of contaminants and pathogens have been removed from the advanced process making the water meet and exceed all California primary and secondary drinking water standards.

How safe is purified water?

The Santa Clara Valley Water District is the primary water resources management agency for Santa Clara County responsible for meeting the county’s water supply demands. To achieve this, the water district plans to produce up to 24,000 acre feet (AFY) per year of highly purified water for potable reuse by the year 2025. This amounts to 8 billion gallons a year of new fresh water that’s drought-proof — enough water to serve 74,000 households each year in Silicon Valley that we would not otherwise have.

The Silicon Valley Advanced Water Purification Center (SVAWPC), which opened in March of 2014, receives secondary-treated wastewater and uses microfiltration, reverse osmosis, and ultraviolet light disinfection to produce highly purified water that meets all California Primary and Secondary Drinking Water Standards. The purified water produced by the SVAWPC is not currently used for potable (i.e., drinking) purposes, but instead is blended with tertiary-treated recycled water and used for a variety of non-potable purposes such as landscaping, agriculture and industry.

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What are the current California drinking water standards and how do they compare with the Purification Center’s water?

The Division of Drinking Water under the California State Water Resource Control Board regulates public drinking water systems (for a copy of latest drinking water standards visit: The SVAWPC facility is currently not licensed for drinking water. However, the plant’s finished water quality meets ALL California Primary and Secondary Drinking Water Standards (a.k.a. as “Maximum Contaminant Levels”). The facility is currently a demonstration plant undergoing continuous improvements to prove to ourselves, our regulators, and the public we serve that we can consistently and reliably produce safe clean drinking water over the long run (including removal of any chemical of emerging concern). In the meantime, plant operators are also evaluating, testing, piloting modeling, and designing future expanded uses of purified water such as groundwater recharge.

What are the benefits of using purified water?

Some important benefits include creating a locally controlled, sustainable, and high-quality water supply and increasing water reliability because purified water is drought proof. Purified water also reduces dependency on water from the Sacramento-San Joaquin River Delta and helps protect the region’s groundwater supplies and environment. Recycling is good for the environment. The more recycled water we use, the less we need to take out of rivers, streams and groundwater basins. All water on the planet is reused. There exists the same amount of water on the plant as there always has been. Water is too precious a resource to use only once!

What are the three phases of advanced water purification?

The treated effluent – already having gone through a two-step advanced process and safe enough for release to the San Francisco Bay — is further purified using three advanced purification processes: microfiltration, reverse osmosis and ultraviolet light.

In this initial filtration process, treated effluent is forced through filtration membrane modules made up of thousands of hollow fibers, similar to straws. These fibers have very fine pores in the sides that are 0.1 micron in diameter, or about 1/300th the width of human hair. As the water is drawn through the pores into the center of the fibers, solids, bacteria, protozoa and some viruses are filtered out of the water.

Reverse Osmosis
During the reverse osmosis (RO) process, water is forced under high pressure through membranes with holes so small that a water molecule is essentially the only substance that can pass through. The process removes constituents such as salts, viruses and most contaminants of emerging concern, such as pharmaceuticals, personal care products and pesticides.

Ultraviolet Light
Now the water is very clean, but as a further safety back-up, the water is sent through chambers that emit strong ultraviolet light to inactivate any remaining viruses and break down some of the remaining trace organic compounds. Ultraviolet light is a powerful disinfection process that creates water of very high quality. The technique is often used to sterilize medicines, food and fruit juices.

What is the difference between indirect and direct potable reuse?

Indirect Potable Reuse (IPR) – is adding purified water to augment groundwater or surface waters. Groundwater and surface waters are considered natural buffers before final treatment and distribution into the drinking water system.

Direct Potable Reuse (DPR) – is the delivery of purified water to a drinking water plant or a drinking water distribution system without an isolating environmental buffer.

What are the steps to purify recycled water?

A multi-barrier treatment process uses advanced technology to replicate the natural water cycle, only faster. This is being done at the Silicon Valley Advanced Water Purification Center (SVAWPC). The water purification process includes microfiltration, reverse osmosis, and ultraviolet light disinfection. An additional final Advanced Oxidation UV step would be added to the purified water if it were to be used for more than traditional recycled water uses such and to be used to augment drinking water supply, which is regulated by the Division of Drinking Water under the State Water Resources Control Board.

What is the difference between purified water and recycled water?

Recycled water generally refers to treated domestic/ municipal wastewater that is used more than once for a beneficial purpose before it passes back into the water cycle. Purified water is highly recycled water that has passed through another proven advanced water treatment process (advanced purification) and has been verified through monitoring to ensure safety for augmenting drinking water supplies.

Will we be drinking recycled water in the future?

Currently, the purified water produced at the SVAWPC is blended with the tertiary-treated water from the San José-Santa Clara Regional Wastewater Facility. This enhances the quality of the recycled water and expands the number of recycled water customers using the water for non-drinking purposes. The purification center is demonstrating proven technologies to produce highly purified water that can be used for various purposes, including expanding future drinking water supplies.

The district is evaluating additional uses for the purified water similar to what is being done by other water districts in the state. For example, Orange County Water District in Southern California recharges its groundwater supply with purified recycled water. The water purified at their Groundwater Replenishment System is the purest water source available, and actually improves groundwater quality.

Isn’t recycled water already part of our drinking water supply?

The water we use today has been used throughout eons, over and over again. In our county, about 40 percent of the water used is imported through the Sacramento-San Joaquin Delta. While nearly all of this water is from rainfall and snowmelt, a small percentage is used by several cities on its way to us and is returned to the system. Our Delta water supplies are treated at one of our three water treatment plants or filtered through groundwater recharge, making it safe to drink.

Is recycled water safe for use?

Yes. The California Department of Public Health allows irrigation and industrial uses of recycled water and even full body contact with recycled water that is part of a recreational lake. However, water from the new Silicon Valley Advanced Water Purification Center will be even purer than traditional recycled water. In fact, highly purified water produced at the center matches and in some cases even exceeds California and federal drinking water standards.

Is recycled water already used in the county?

Yes. Recycled water has been successfully used in Santa Clara County since the 1970s and currently comprises almost 5 percent of the county’s water supply mix. Tertiary-treated recycled water is used for a variety of non-drinking purposes such as landscaping, agriculture and industrial uses.

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