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Purified Water

What is purified water?
Purified water (or advanced purified water) passes through treatment processes that have been proven and monitoring processes that have been verified for the safe augmentation of drinking water supplies. Often source water used to produce purified water comes from a wastewater treatment or resource recovery plant. The purification may include several stages such as microfiltration (or ultrafiltration), reverse osmosis and advanced oxidation. They can also include Soil Aquifer Treatment. The result of these processes is a highly purified, clean water source.

Who regulates purified water? What laws and regulations must be met?
In California, the permits for the use of recycled water are granted by the State Water Resources Control Board (SWRCB) and its nine Regional Water Quality Control Boards (RWQCB). In July of 2014 the regulatory authority was moved from the California Department of Public Health (CDPH) to the SWRCB, which now reviews and establishes water recycling criteria and regulations. These regulations are among the most stringent in the world. The permits incorporate these recommendations and other conditions for the safe use of recycled water.

What does the advanced water purification process remove?
Advanced water treatment processes that utilize membrane filtration, reverse osmosis, UV treatment and hydrogen peroxide remove contaminants to levels below concentrations of significance. Ultrafiltration removes particulate matter, bacteria, and protozoa. Reverse osmosis removes viruses, dissolved salts, pesticides, and most organic compounds. Advanced oxidation through ultraviolet light combined with sodium hypochlorite sterilizes and eliminates organic compound traces in water. These purification treatment processes can produce water qualities that are equal to or better than existing drinking water sources.

Is advanced purified water safe for drinking?
Yes, the purified water produced from advanced purification processes can meet or exceed the same rigorous state and federal standards required for all drinking water. However, the purpose of the PureWaterSF project is primarily research to test the reliability and gather data on a building-scale purification process.

If purified water is so clean, why can’t we introduce it straight into the taps?
This project is intended for research only, with the goal of collecting data that can inform a broader, statewide dialogue on purified water use. The data will help demonstrate how reliable these advanced treatment systems are and the water quality that results on a building scale. The State of California is considering regulations for this type of potable reuse project. These regulations would ensure that public health will always be protected as new types of potable reuse projects are being considered by communities.

What is the cost of purified water?
The cost of purified water can vary greatly depending upon where it is produced and what source water is being used to produce it. Grant funding can also offset costs of purified water production, which is the case for example at the Orange County Water District. Some estimates, such as that of Pure Water San Diego include a range from $1700-1900 per acre-foot that equates to less than one penny per gallon. With the current cost of imported water in some places in California expected to double in the next ten years, water purification may ultimately be a more cost-effective option.

What are the benefits of using purified water?
The benefits of using purified water are many but may vary in different regions. Benefits may include:

  • Decreased dependency on imported water
  • A locally controlled, reliable supply of high-quality water that is drought resistant
  • Sufficient water supplies to support economic vitality
  • High-quality water to replenish groundwater basins
  • Reduction of the amount of wastewater discharged to creeks, rivers and bays
  • A source of water for seawater intrusion protection
  • A more diversified water supply

Water Reuse

What is water reuse?
There are two main types of water reuse: reuse that refers to the use of non-potable water (often used for activities like landscape watering, toilet flushing, street cleaning, and irrigation), and reuse that refers to potable water use (used in drinking water systems). In both cases, water undergoes different cleaning or treatment processes that bring the quality of the water up to certain standards depending on how the water will be used. Potable water reuse requires more advanced treatment that brings the water up to drinking-water standards, enabling the water to be used for activities like bathing and drinking (see more information in the Purified Water FAQ section).

What is the difference between indirect and direct potable reuse?  
How potable reused water is delivered determines if it is called indirect potable reuse or direct potable reuse. Indirect potable reuse means the water is delivered to you indirectly. After it is purified, the reused water blends with other supplies and/or sits a while in some sort of manmade or natural storage before it gets delivered to a pipeline that leads to a drinking water plant or distribution system. That storage could be a groundwater basin or a surface water reservoir. Direct potable reuse means the reused water is put directly into pipelines that go to a drinking water plant or distribution system. Direct potable reuse may occur with or without “engineered storage” such as underground or above ground tanks.


What is unique about the PureWaterSF project?
This project will use innovative building-scale treatment, proven purification processes, real time online monitoring, and advanced analytical tools. This project will demonstrate how advanced water purification and monitoring technologies can reliably convert building-sourced wastewaters into a high-quality supply to meet diverse end uses.

Why is this research important for San Francisco?
San Francisco’s infrastructure is unique. There are water treatment and storage facilities within the Regional Water System. However, there is no water treatment plant nor extra water storage facility within the City limits. The combined water system (which takes wastewater and stormwater into the same pipes) produces lots of wastewater. The PureWaterSF research project helps us investigate options for the future, sustainable use of this water source, testing the reliability of smaller scale systems and the ability of these systems to meet high quality standards.

Is the purified water added to our drinking water?
No. The purified water for the PureWaterSF project will be produced and monitored for research purposes only and then returned to the recycled water system for toilet flushing.

How is the PureWaterSF project important for purified water/water reuse in general?
In the bigger picture, the PureWaterSF project provides a novel approach for local water treatment while gathering much needed data to bridge current knowledge gaps in water reuse/purified water treatment processes. The advanced analytics conducted in the monitoring and sampling procedures of this project give insight into how we can monitor and manage these new purifying treatment processes in real time. It is anticipated that, by gathering a greater data base and filling in these gaps, we will have sound evidence to better inform future policy and regulations surrounding these systems and more localized water treatment in general.

Last updated: 12/12/2019 3:26:30 PM