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.

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.

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.

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

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.

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.

Microfiltration
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.

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.

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: https://www.waterboards.ca.gov/drinking_water/programs/index.shtml). 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.

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.

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.