But the safety of direct reuse of recycled wastewater is still being studied, and US regulations so far do not allow that.
The technology for these buildings to capture and treat all their water to potable standards already exists. By 2040, the agency says, its Onsite Water Reuse program will save 1.3 million gallons of potable water each day. The San Francisco Public Utilities Commission, the water provider, estimates that there are a total of 48 reuse systems in operation and 29 more projects being planned in the city. (In New York, the Domino Sugar Refinery redevelopment project, currently under construction on the Brooklyn waterfront, will recycle 400,000 gallons of black water a day.) Outside water is still needed for potable uses. That’s the equivalent of the annual use of 16,000 San Franciscans, the company says. Built by the Australian company Aquacell, the system cleans 30,000 gallons of sewage, sink, shower, and other wastewater each day and uses it for irrigation and toilet flushing, saving an estimated 7.8 million gallons of water a year. The largest building with an onsite system is the Salesforce Tower, a 61-story office, hotel, and residential tower that opened in 2018 and is the tallest building in San Francisco. San Francisco’s recycling systems are not water-neutral. “It’s a slow-moving process, but at the end of the day-considering all the scarcity-a lot of communities are going to pick this up as a way of having economic development while having water security.” “This is the future of water for everybody,” said Newsha Ajami, director of Urban Water Policy at Stanford’s Water in the West program, of decentralized water systems and recycling. By 2050, the UN estimates that 5 billion people could be subjected to water shortages. A recent study found that more than half the world’s lakes have lost significant amounts of water over the past 30 years. There are serious pressures on fresh water supplies around the world, with climate change exacerbating shortages. And decentralized projects are ongoing in Japan, India, and Australia.
With the mega-drought and water crisis on the Colorado, the Rio Grande, and other Western rivers, “extreme decentralization” is making its way to other places in the American West, including Colorado, Texas, and Washington State. To demonstrate its technology, Epic Cleantec, a water recycling company, has even brewed a beer called Epic OneWater Brew with purified gray water from a 40-story San Francisco apartment building. Using recycled water for showers would eliminate another 20 percent of water demand, though the safety of that practice is being researched, and it is not yet permitted in San Francisco. Using it to flush toilets and wash clothes reduces demand for new water by about 40 percent. Recycling gray water alone can save substantial amounts of water. The process reduces the building’s imported potable supply by 40 percent. (Black water comes from toilets, dishwashers, and kitchen sinks gray water comes from washing machines, showers, and bathtubs.) The headquarters of the San Francisco Public Utilities Commission has a black-water system, called the Living Machine, that treats its wastewater in engineered wetlands built into the sidewalks around the building, then uses it to flush low-flow toilets and urinals. So far, six black-water and 25 gray-water systems are using the technology, and many others are in the works. Proof of concept is unfolding in San Francisco, which in 2015 required all new buildings of more than 100,000 square feet to have onsite recycling systems.
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