On-site water treatment as an alternative water supply: Opportunities and challenges
Paula Kehoe discusses how San Francisco’s implementation of on-site water treatment systems in large buildings is saving millions of gallons of water per year
At the National Water Research Institute’s Drought Response Workshop 2015, Paula Kehoe, Director of Water Resources with the San Francisco Public Utilities Commission, gave a presentation on how San Francisco is implementing on-site treatment systems in large buildings to generate water for non-potable uses, such as toilet flushing and irrigation, saving millions of gallons per year in the process.
Ms. Kehoe began by giving some background information on the San Francisco Public Utilities Commission (SFPUC). “The SFPUC is a department within the city and county of San Francisco,” she said. “We operate three separate enterprises: a water enterprise, a wastewater enterprise, and a power enterprise. Within our water enterprise, we provide water to 2.6 million people in the San Francisco Bay Area – all of San Francisco as well as 1.8 million people outside San Francisco for whom we provide wholesale services. We operate a combined sewer system in San Francisco, which means we collect and treat both the stormwater and wastewater prior to discharge to the San Francisco Bay and the Pacific Ocean. And within our power enterprise, we generate both hydroelectric and solar power, and we use that power to serve our city facilities, such as City Hall, San Francisco Airport, etc.”
She presented a slide of the city’s water system, noting that 85% of their water comes from the Tuolumne River, which is stored in the Hetch Hetchy Reservoir located within Yosemite National Park; the water travels 167 miles all by gravity to San Francisco. The remaining 15% of our water comes from reservoirs that are located in the East Bay as well as the peninsula, she said, noting that they blend their water supplies and serve all of their customers.
She pointed out the water system crosses three major earthquake faults: On the East Bay, the Hayward Fault, and the Calaveras Fault, and then on the peninsula, the San Andreas Fault. “Many portions of our system are built in the early 1900s, and it crosses major earthquake faults so we’ve been actively working on a major capital improvement program designed to repair and replace many portions of our infrastructure. The program has a cost of $4.8 billion, and we’re approximately 80% complete with the program.”
Ms. Kehoe said they have a comprehensive conservation program to reduce customer demand as well as to develop new local water supplies. “Prior to the drought, San Francisco was at 49 gallons per person per day on a residential scale; Of course, we don’t have a lot of outdoor irrigation use in San Francisco, so I always give that caveat that we have the pleasure of not having a lot of outdoor grass to keep our per capita relatively low. We made the call for voluntary rationing for all of our customers at 10%, that goal was a savings of 8 billion gallons, and we did exceed that goal, we saved close to 9 billion gallons.”
Ms. Kehoe said they are also developing groundwater supplies for both normal and dry years, noting they had recently reached a construction contract for installing six groundwater wells to pump groundwater from the west side of San Francisco and to blend that with surface water supplies. They are also working on a conjunctive use project south of San Francisco, as well as developing recycled water for both irrigation and toilet flushing. They have competed two recycled water projects and are proposing to build a recycled water treatment plant in the city & county of San Francisco, she said.
As another way of developing new local supplies, the SFPUC has turned their attention to the potential water supplies that are developed and produced by buildings. “Buildings actually produce a number of non-traditional sources of water or alternate water sources,” she said. “They produce rain water – water that hits our roof; buildings also produce stormwater – water that hits our streets, sidewalks and parking lots, and in San Francisco, we have a number of buildings that are actually pumping groundwater or foundation drainage which is useless groundwater to prevent flooding in their basements. That water goes directly into the sewer system, so again we have an ample of supply of foundation drainage in the city.”
“Buildings also generate gray water, which in California is defined as water from our clothes washers, our bathroom sinks and showers. And finally buildings produce black water, which is gray water plus water from our toilets, dishwashers, kitchen sinks, and utility sinks,” she said.
Ms. Kehoe said they spent some time researching onsite, decentralized water systems, and found that there are a lot of onsite water treatment systems implemented throughout the world. “The collection and treatment of alternate water sources for non-potable applications are happening in green buildings, they are happening in districts, they are happening in neighborhoods, and in urbanized areas throughout the world,” she said. “These onsite systems produce non-potable water for many applications within a building or district, such as toilet flushing, irrigation, and cooling tower. And most often, the onsite decentralized systems are integrated with the centralized water and wastewater infrastructure without negatively impacting the centralized systems.”
Ms. Kehoe pointed out that many of these projects have been operating for decades. “Battery Park located on the southwest tip of Manhattan has a number of buildings that have treatment plants in the basement of the building where they are collecting the water within the building and using that to flush toilets within the building or within the district in Battery Park,” she said, noting that many of these projects have been in successful operation, some even achieving a 75% reduction in potable water use.
Ms. Kehoe said there is a lot of construction currently going on in San Francisco, so they wanted to think about the role of onsite water treatments within buildings and in districts in San Francisco as well as building design and to really reimagine how water is used. “So when it came to building our new headquarters, the San Francisco PUC incorporated two onsite water treatment systems,” she said. “We have installed a ‘living machine’, which is a patented trademarked technology that treats the wastewater, so we are treating the wastewater on the sidewalk of our building. It’s unique in terms of actually treating wastewater in the public right of way, but you cannot come into contact with the wastewater. The water is treated through the wetland cells, and then we use UV and chlorine as a disinfectant prior to reusing the water within the building to flush our toilets and our urinals.”
She noted that they also have a rainwater harvesting system collecting rain water from the roof and a stormwater collection system in the back of the building that collects water that is treated and used for irrigation.
These systems have resulted in significant water savings, she pointed out. “We’ve been able to reduce our consumption of potable water in the building by 40%, or in terms of gallons, we’ve saved over 1.5 million gallon each years for the past two years.”
Other developers in San Francisco became interested in implementing similar systems in their buildings, but there were a number of regulatory issues associated with the collection and treatment of alternate water sources for non-potable application, she said. “For example, who sets the water quality standards, who actually issues permits and provides operational oversight, and what kind of ongoing monitoring and reporting is required and should be implemented?”
The uniform plumbing code was updated in 2013 which included expanded onsite gray water and rain water standards, as well as construction requirements, but it did not include any management or ongoing oversight with decentralized water systems. “In San Francisco, we were encouraging onsite applications as we certainly saw an opportunity to save additional potable water in the city, so it required us to develop a program on a local level within the city,” Ms. Kehoe said. “So we developed a city ordinance. We actually modified the public health code, and the ordinance which was passed in late September 2012. It initially focused just on an individual building, but we later amended it in 2013 to allow for district scale applications and a district scale, which is defined as more than 2 buildings that can either share or sell the water between each other, but the ordinance is fundamentally the same, whether it’s on a building scale or a district scale.”
The ordinance involved three city departments: the San Francisco Public Utilities Commission, the San Francisco Department of Public Health, and the San Francisco Department of Building Inspection. “The role of the San Francisco Public Utilities Commission was program administration,” Ms. Kehoe said. “We were looking at helping architects, engineers and developers understand what kind of potential potable and non-potable demands in their building. We track potable offsets, we provide technical support, and provide financial incentives.”
“The role of the San Francisco Department of Public Health is extremely critical in this program; they actually will issue a permit to the owner of the onsite water treatment system; they also establish water quality standards and monitoring requirements, and they review water quality reporting,” she said. “The role of the Department of Building Inspection in San Francisco is just as critical. They actually inspect and approve the installation of any of these systems.”
She then touched on some of the details, noting that they spent a lot of time debating and talking about some of these. “We do not allow any system to be off the grid; any onsite water treatment system, whether in it’s in a building or a district, it must be connected to the potable system as well as the wastewater system, and we require the same backflow protection requirements as potable.”
In terms of the system construction, purple pipe needs to be used inside the building, it just needs to be labeled appropriately, whether it’s recycled water or onsite and untreated potable water, and signage is required throughout the building, inside any equipment room, and outside if used for irrigation, she said.
Water quality was a big topic that generated quite an amount of debate, she said. “For black water systems, there aren’t any regulations or water quality standards, so what we opted to do was we opted to use the same standards as Title 22,” she said. “In terms of gray water and rain water, the California plumbing code did come up with standards, so that was very helpful. In terms of the water quality standards for stormwater and foundation drainage, there aren’t any existing state standards, so we in San Francisco developed our own standards.”
Ms. Kehoe reiterated that the local Department of Public Health will actually issue a permit to operate the system and require ongoing monitoring and reporting. “Rainwater has less frequent monitoring requirements; moving; from rainwater to stormwater to foundation drainage and gray water, the frequency becomes more frequent, and then ultimately black water systems.”
The San Francisco PUC has developed a guidebook to provide technical assistance, as well as a grant program, which provides up to $250,000 for individual building applications that save at least 1 million gallons of potable water per year for 10 years, and up to $500,000 for district-scale applications that save at 3 million gallons a year for 10 years. They have also developed a water use calculator to help engineers and architects understand the potable and non-potable indoor water demands, and if they should be using gray water, black water, or foundation drainage. “All of the building needs and available water supplies are really site specific,” Ms. Kehoe pointed out.
Currently, 20 projects have submitted applications to collect a variety of alternative water sources for non-potable application. She gave some examples:
Ms. Kehoe said they are collecting data on all of these projects, which is available in a profile report online. “We are really interested in understanding a lot of details about these projects,” she said. “We want to understand the drivers. What are the drivers for a project for an architect or a property owner to collect and treat alternate water sources? How much do these systems costs? What is the annual O&M, what kind of end uses are they taking, what types of water are they collecting and treating? Unfortunately we don’t have a lot of O&M data at the moment because a lot of these systems haven’t been online long enough, but this report is constantly updated.”
In 2014, the San Francisco Public Utilities Commission and the Water Environment Research Foundation hosted a meeting in San Francisco with other public agencies from across the country, as well as Canada to talk about the challenges associated with onsite water systems in their communities. “What we found that we had very similar issues, and really the meeting confirmed our two biggest issues, which are how do you manage these systems from a public agency perspective, and what’s the appropriate water quality standard.”
To address the issue of managing the systems, the San Francisco PUC has developed a blueprint or guide that includes 10 steps to develop a program on the local level to deal with onsite water treatment systems. To address the issue of water quality standards, they have established a multi-state public health collaborative with officials from the state of WA, OR, HI, Minnesota, as well as public health departments in Los Angeles, San Francisco, and New York City. “The goal of this project is to establish consensus in terms of the appropriate water quality standards and monitoring regimes. Monitoring regimes are really important, whether it’s a Title 22 standard, an NSF 350 standard, that could be debated, but the issue about appropriate monitoring and reporting still needs to be discussed. We plan to initiate that effort in the next month.”
“If you are interested in more information on our program, you can go online. All the materials are available on our website … “
For more information …
- For a multitude of resources, reports, and other information on San Francisco’s Non-potable water program, click here.
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