Frequently Asked Questions About Advanced Water Purification

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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.

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

The water district is responsible for securing, managing and delivering a safe and reliable water supply to the region. Searching for sustainable local water supply sources that match the right quality with the right use is part of that responsibility.

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.

This will allow the water district to apply proven technologies to produce purified water, expanding the options for recycled water uses throughout the region.

The $72 million purification center in San José will produce up to 8 million gallons of highly purified water per day, making it the largest advanced water purification plant in Northern California.

Why can’t we just conserve enough water to meet future needs?

Water conservation will remain important to preserving the county’s precious water supplies. Since the late 1980s, the county’s population has increased by about 25 percent, while our water use has remained relatively flat despite a growing economy.

However, conservation alone is not enough to meet our current and future water needs. Climate change, recurring droughts and regulatory restrictions all place growing pressures on the state’s water supplies and underline the need for new sources of water. Our current sources, combined with expanded water conservation and recycling, are necessary if Silicon Valley is to continue to thrive.

Will we be drinking recycled water in the future?

At this time the purified water will be blended with the water produced at the San José-Santa Clara Regional Wastewater Facility. This will enhance the quality of the recycled water produced there and expand the number of recycled water customers using the water for non-drinking purposes.

The purification center will demonstrate proven technologies that are available locally to produce highly purified water that can be used for various purposes, including expanding future drinking water supplies.

In the future, the district may evaluate additional uses for the purified water similar to that being done by other water districts in the state. 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.

No decision has been made to implement such a project locally. Such a decision would only be made after an extensive public engagement process.

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

The water we use today has been used 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 is expected to match California drinking water standards.

What are the three phases of advanced water purification?

The new advanced water purification center will use technology similar to Mother Nature’s filtration process, but with the advantage of purifying the water more quickly, making it the product of one of the world’s most highly developed purification processes. This process and other comparable processes are used successfully to produce clean, safe drinking water throughout the world.

The treated effluent--already having gone through a two-step advanced process and safe enough for release to the San Francisco Bay—will be further purified using the 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 almost 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.