PureWaterSF FAQs

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.

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.

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.

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.

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.

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.

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

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).

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.

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.

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.

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.

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.

This list of terms and definitions borrow directly from the State Water Resources Control Board (SWRCB)’s Division of Drinking Water Terms and Definitions for Potable Reuse. This was put together by the Advisory Group on Direct Potable Reuse. 

Advanced Treatment: This term is often used to mean additional engineered treatment after secondary or tertiary treatment of wastewater to remove contaminants of concern to achieve public health or specific beneficial reuse parameters. However, the amount and type of advanced treatment applied is subject to the application, site-specific parameters, and federal, state, or local regulatory requirements.

Advanced Oxidation Process (AOP): A set of chemical treatment processes whereby oxidation of organic contaminants occurs on a molecular level through reactions with hydroxyl radicals. The advanced oxidation process typically employs hydrogen peroxide, hypochlorite, ozone and/or ultraviolet light, which break down organic molecules into metabolites.

Constituents of Emerging Concern (CECs): Chemicals or compounds not regulated in drinking water or advanced treated water. They may be candidates for future regulation depending on their ecological toxicity, potential human health effects, public perception and frequency of occurrence.

Direct Potable Reuse (DPR): The delivery of purified water to a drinking water plant or a drinking water distribution system without an environmental buffer. Additional treatment, monitoring, and/or an engineered buffer(s) would be used in place of an environmental buffer to provide equivalent protection of public health and response time in the event that the purified water does not meet specifications.

Drinking Water: Water conveyed through pipelines to homes and businesses that is safe for human consumption and meets all federal, state, and local health authority drinking water standards. Water treatment and distribution facilities that produce drinking water require an operational permit issued by the federal, state, or other designated permitting authority.

Filtration: A process that separates small particles from water by using a porous barrier to trap the particles while allowing the filtered water to pass through.

Indirect Potable Reuse: The addition of recycled water to augment groundwater or surface waters. Groundwater and surface waters are considered environmental buffers for providing public health protection benefits, such as contaminant attenuation dilution, and time to detect and respond to failures before final treatment and distribution. Indirect potable reuse can used advanced treated water, but can also be accomplished with tertiary effluent when applied by spreading (i.e., groundwater recharge) to take advantage of soil aquifer treatment (SAT).

Non-potable Reuse: Includes all recycled or reclaimed water reuse applications except those related to water supply augmentation and drinking water (i.e., potable reuse).

Pathogen: A microorganism (e.g. bacteria, virus, Giardia or Cryptosporidium) capable of causing illness in humans.

Potable Reuse: A general term for the use of recycled water to augment drinking water supplies. Potable reuse, which covers both indirect and direct potable reuse, involves various forms of treatment options. Potable reuse can be the addition of advanced treated recycled water or purified water to augment a drinking water supply. This form of potable reuse utilizes advanced treatment technology in combination with either environmental or engineered buffers to ensure that all necessary public health requirements are met to allow the water to be used as a drinking water supply. Potable reuse can also be accomplished with tertiary effluent when applied by spreading (i.e., groundwater recharge) to take advantage of soil aquifer treatment (SAT).

Purified Water: Water that has passed through a wastewater treatment plant and a full advanced treatment plant, and has been verified through monitoring to be suitable for augmenting drinking water supplies.

Recycled Water: Water that is used more than one time before it passes back into the water cycle. For example, wastewater that has been treated to a level that allows for its reuse for a beneficial purpose such as irrigation. Recycled water is sometimes called “reclaimed water.” With additional treatment, including advanced treatment, recycled water can be used as a source of water for a drinking water supply (see potable reuse).

Reliability: The ability of a treatment process or treatment train to consistently achieve the desired degree of treatment, based on its inherent redundancy, robustness, and resilience.

Reverse Osmosis: A high-pressure membrane filtration process that forces water through semi-permeable membranes to filter out large molecules and contaminants, including salts, viruses, pesticides, and other materials.

Title 22 Standards: Requirements established by the California Department of Health Services for the production and use of recycled water. Title 22, Chapter 3, Division 4 of the California Code of Regulations, outlines the level of treatment required for allowable uses for recycled water.

Ultrafiltration: Ultrafiltration is a type of membrane filtration in which hydrostatic pressure forces a liquid against a semipermeable membrane. A semipermeable membrane is a thin layer of material capable of separating substances when a driven force is applied across a membrane.

Ultraviolet (UV) Disinfection: UV disinfection is a cost-effective and reliable technology that protects against pathogenic organisms. This includes protozoa, bacteria, and viruses. (adapted from Treatment Plant Operator Magazine).

Water Reuse/Recycled Water: Water recycling is reusing treated wastewater for beneficial purposes such as agricultural and landscape irrigation, industrial processes, toilet flushing, and replenishing a ground water basin (referred to as ground water recharge). Water recycling offers resource and financial savings. (US EPA , Water Recycling and Reuse) The terms “reused” and “recycled” are often used interchangeably depending on where you are geographically.