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Purpose Objectives Fact Sheet System Schematic


Purpose of the PureWaterSF Research Project

The PureWaterSF project is a research project that explores how we can treat and reliably produce purified water on a small (building) scale using wastewater generated onsite. For this project, the SFPUC will be taking approximately 80% of the recycled water currently produced by the constructed wetland treatment system called the Living Machine™ at the SFPUC headquarters. The PureWaterSF process will further purify this water, bringing it to a level that is expected to meet or exceed drinking water standards.

Data from this process will be collected and analyzed, and the water produced will be returned to the building’s non-potable (non-drinking water) system for toilet flushing. 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 project will also adhere to and help inform future California potable reuse regulations.

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Research Objectives

The goal of this research project is to demonstrate how advanced water purification and monitoring technologies can reliably convert building-sourced wastewaters into a high-quality supply to meet diverse end uses. Several objectives help us achieve this goal:
  1. Examine reliability of a water purification system at building-scale
    The research examines the reliability of a purification system measuring common parameters such as chlorine, pH, turbidity (how clear the water is), and temperature. This information is regularly collected using real-time monitoring and provides valuable information about the reliability of these systems at a building level.
  2. Create a research baseline through advanced water quality analytics
    The project follows recommendations from state experts to use specific water quality analytics to address knowledge gaps in the industry. These analytics include nontarget analyses (NTA), which measure substances we have not typically measured or created targets for before, and biological assessments, which can test the overall level of bioactivity in water samples. Data from this research can help inform statewide regulatory deliberations.
  3. Promote transparent science through outreach and communication
    The project focuses on promoting transparent scientific practices through outreach and communication by using: factsheets, a digital wall display, a digital tour video, in-person tours and this website. All of these components work toward fostering a greater understanding of purified water in our communities. Public feedback will further inform future work by the SFPUC.
  4. Provide new opportunities with on-site operator training
    PureWaterSF provides a unique opportunity for operators to receive onsite training with a building-scale water purification system at the SFPUC headquarters. Operator feedback will help inform planning and system development.

If you would like to learn more about purified water research in San Francisco, sign up for our email list here!

We'd like to know what you think about PureWaterSF, click here to take a short survey.

Register here to tour the PureWaterSF Research Project at 525 Golden Gate, SF.

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Living Machine System Schematic

The Living Machine™ is a constructed wetland system providing on-site non-potable water reuse at the SFPUC Headquarters (SFPUC HQ). It collects and treats the building’s wastewater and reuses this water for toilet flushing. The system has a capacity of 5,000 gallons per day.

Living Machine schematic

The Living Machine™ has several main system components that move and treat the building’s wastewater as follows:

  1. Primary Tank: wastewater is first sent to a primary treatment tank where sewage is settled and screened using a trash and a settling chamber to separate larger solids. The filtered wastewater then flows to the Equalization and Recirculation Tanks.
  2. Equalization and Recirculation Tanks: filtered wastewater is then sent to the Equalization Tank which holds back the wastewater and acts as a buffer until it can be sent to the Recirculation Tank. The Recirculation Tank doses the wetlands with a steady flow of wastewater throughout the day.
  3. Tidal Flow Wetlands: The Tidal Flow Wetlands are located outside the SFPUC headquarters along Golden Gate Avenue. These are designed to mimic natural tidal wetlands. Water from the Recirculation Tank fills the wetland planter boxes from the bottom up, and then water is drained by gravity back to the Recirculation Tank. Gravel media in these planters enables the growth of a healthy biofilm that is home to a diverse population of microorganisms which feed on nutrients in the wastewater. The planters are filled and drained 12 times a day.
  4. Polishing Vertical Flow Wetlands: at the end of the 12 cycles, the effluent is sent to the Vertical Flow Wetlands where remaining organic material and nitrogenous compounds are removed.
  5. Disinfection: The water is then sent through a disinfection process where it is filtered to remove solids and reduce turbidity, sent through an ultraviolet unit to deactivate bacteria and viruses, and sent through a chlorination tablet feeder to prevent growth in the building’s recycled water pipes.
  6. Recycled Water Tank: After the above treatment process is complete, the water is stored in the Recycled Water Tank and is used for toilet and urinal flushing.

Treated water held in the Recycled Water Tank is also now being used as source water for the PureWaterSF research project where the water undergoes advanced treatment up to potable standards and is analyzed for research purposes before being returned to the building’s non-potable system. Please see the Living Machine™ link for further information.


Did You Know ...


  • The Living Machine is one of the first buildings in the nation with onsite treatment of grey and black water to be recycled for toilet-flushing?
  • The Living Machine reduces the SFPUC headquarters’ water use by about 65%, saving 800,000 gallons of water per year?
  • Wetlands are often less expensive to build than traditional wastewater and stormwater treatment options, have low operating and maintenance expenses and can handle fluctuating water levels (USEPA, 2006).

PureWaterSF System Schematic

The PureWaterSF system will add an advanced water treatment system onto the existing engineered wetland system of the SFPUC’s Living Machine™. The PureWaterSF system takes this already treated water and purifies this to generate (approximately) 1,296 gallons per day of highly purified water at a rate of about 0.9 gallons/minute. This high-quality water meets drinking water standards using the most advanced purification processes available including ultrafiltration, reverse osmosis, and ultraviolet light with advanced oxidation.

Living Machine schematic


  1. Ultrafiltration: After initial water quality sampling and testing, the water taken from the Living Machine™ first goes through ultrafiltration (UF) which involves passing recycled wastewater through very fine hollow fiber membranes and removing particulate matter, bacteria, and protozoa. After passing through the membrane, the filtered water mostly contains dissolved salt and organic molecules. Sampling: UF effluent is sampled for chloramines, free chlorine, nitrate, TOC, DOC, UV254, and turbidity.
  2. Reverse Osmosis: The next step is reverse osmosis (RO) where the water is pushed through a semi-permeable membrane at high pressure to remove impurities such as viruses, dissolved salts, pesticides, and most organic compounds. It is the same process used to desalinate seawater. Sampling: RO permeate is sampled for TOC, nitrate, nitrite, turbidity, pH, temperature, free chlorine, and UV254.
  3. Ultraviolet Light with Advanced Oxidation: The final step is ultraviolet light with advanced oxidation which exposes the water to ultraviolet (UV) light combined with sodium hypochlorite to disinfect any pathogens and to further reduce chemicals to non-detectable levels. Sampling: The finished water is sampled for free chlorine and UVT.
  4. The SFPUC’s living machine has treated building wastewater for non-potable reuse since 2012. The machine treats roughly 5,000 gallons per day, saving roughly 800,000 gallons per year (over 60% reduction in total water use). Through the PureWaterSF project, roughly 80% of the Living Machine effluent will be purified to a level comparable to drinking water standards. The purified water will continue to be fed into the building’s non-potable distribution system.

Did You Know ...


  • Advanced purification processes are already being used to recycle and reuse water on spaceships, and cruise ships? Even at Disneyland!
  • In California alone, there are 9 other purified water projects underway including in Santa Clara, Los Angeles, Orange County, and San Diego?
  • By 2027, the volume of recycled water produced in the United States is projected to increase 37% from 4.8 billion gallons per day to 6.6 billion gallons per day (WaterReuse, 2018)?

Downloadable Fact Sheets on the project are available here:

Technical Information

General Information


PureWaterSF System Performance & Reliability

Ensuring Reliable System Performance: Water testing is conducted at every step to ensure that each element of our system is efficiently and effectively removing the microorganisms it was designed to remove. This testing assesses the system’s performance in terms of the overall reliability of the system, and how well the system is able to continuously achieve water quality standards. Grab samples will be taken at regular intervals and analyzed for conventional water quality parameters, such as pH, chlorine, and hardness, as well as for potential contaminants, such as pharmaceuticals, bacteria or viruses.

At the end of the approximately 30-minute process, we are able to confirm that all the treatment goals are achieved, and we compare the purified water to drinking water standards.

Using Advanced Analytics to detect “unknown unknowns” in our water: We then go one step further to gain a more holistic understanding of the water we are producing. We run a test that can indicate any trace of compounds such as pharmaceuticals and personal care products, which are ordinarily very difficult to detect. For this testing we use advanced data analytics, which includes bioassays (biological assessments) and non-target analysis (NTA) to measure biological effects of various trace level chemicals found in our water system. With this testing, we are trying to go beyond understanding what's been removed toward a better understanding of what remains in the water.

Real-Time Monitoring: While the system runs, it conducts a continuous real-time monitoring to assess system performance and overall reliability. This real-time monitoring assesses the following standard measurements of water quality:

  • TOTAL DISSOLVED SOLIDS - TDS are inorganic salts and organic matter that are dissolved in water. TDS is an indicator of general water quality. The EPA sets a secondary drinking water standard for TDS at 500 mg/L. An elevated level of TDS is not a health hazard.
  • TOTAL ORGANIC CARBON - TOC is a measure of the level of organic molecules or contaminants in purified water. TOC in itself has no health effects but provides a medium for the formation of toxic disinfection by-products.
  • TURBIDITY - Turbidity is the measure of relative clarity of a liquid. Material that causes water to be turbid include clay, silt, finely divided inorganic and organic matter algae, soluble colored organic compounds, plankton, and other microscopic organisms.
  • ULTRAVIOLET ABSORPTION (UVA) - UVA represents the amount of light absorbed by constituents within water (light energy that does not reach the detector). UVA is commonly used as an indicator of general water-quality, or the potential for disinfection by-product formation.
Last updated: 9/17/2019 4:16:16 PM