270 Brannan, San Francisco, CA


270 Brannan, San Francisco, CA


ACCO Engineered Systems


Rainwater and Condensate for Toilet Flushing and Irrigation


March 2016


270 Brannan Street is a 202,000 square foot, Class A office building in the center of San Francisco’s SOMA district. Designed by Pfau Long Architects, the building incorporates the latest in environmentally sustainable design and was seeking LEED Platinum certification. The innovative architecture provides modern appeal while blending seamlessly with the surrounding South End Historic District. Developers were anxious to support sustainability efforts for the project by capturing rainwater run-off and harvesting the source for toilet flushing throughout the building. Wahaso was asked to help design the rainwater harvesting system late in 2013.



Wahaso needed to design a turn-key system that would capture rooftop rainwater into a cast-in-place cistern in the building’s parking area. Pre-filtration would need to be added before the cistern and the system would need to transfer the rainwater to a filtration skid and pumps so that a highly reliable source of safe, clean water would always be available for flushing toilets. The system design would need to pass the tough new requirements for water reuse established by the San Francisco Public Utilities Commission and the San Francisco Public Health Board.


Wahaso’s Water Balance analysis projected that even with 22,000 gallons of rainwater storage, there was not sufficient supply available to meet all the toilet flushing demand. The Wahaso team recommended adding cooling condensate to the supply to help meet demand during the dry season, and condensate was projected to provide over 1,000 gallons per day during peak cooling days. The Wahaso design added a high-capacity cascade filter inside the cistern to remove the majority of suspended solids from the rooftop rainwater flow. The 12” inlet cascades over a 350-micron filter that drops directly into the cistern below. Large flows and filtered debris bypass to the stormwater system, and a self-cleaning final filter and high-energy 50 UVT ultraviolet filter polish and sanitize the rainwater and condensate into a 500-gallon processed water holding tank. Duplex 7.5 HP pumps pressurize the treated rainwater throughout the building. Redundant municipal water back-up adds water to the day tank when the cistern is empty or can be manually diverted to bypass the system entirely in a power failure.


The system is projected to save 400,000 gallons of municipal water per year and meets 100% of irrigation needs as well as 83% of toilet flushing demand for the building. The building was awarded LEED Platinum certification in November 2016 and earned 100% of the LEED points available for water efficiency.

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