270 Brannan

San Francisco, CA



270 Brannan Rainwater & Condensate For Toilet Flushing & Irrigation

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.


Water Supply Sustainability Index (2050)

Project Details


San Francisco, CA


ACCO Engineered Systems


Plumbing Engineer, Civil Engineer, Commercial Contractors, Commercial Architect




Rainwater and Condensate for Toilet Flushing and Irrigation


March 2016

Project Gallery

270 Brannan Rainwater & Condensate For Toilet Flushing & Irrigation

It was critical that most of the suspended solids in the stormwater runoff would be removed before they entered the storage system, so to deliver a complete solution, Wahaso brought in two other partners: SunTree Technologies and Oldcastle Precast. SunTree Technologies recommended their Nutrient Separating Baffle Box system to remove sediment, organic material, and hydrocarbons from large storm flows entering the cistern. The system holds trash above the standing water line and uses a series of baffles to remove suspended solids to less than 350 microns.

Oldcastle Precast supported the design and engineering of the Storm Capture system for this project and was designed to hold 37,000 gallons of pre-treated stormwater below-grade in nine pre-cast modules. Oldcastle also helped to resolve the sightlines requirement by providing an additional module to contain all the harvesting equipment below-grade. An 8’ X 10’ pre-cast equipment room was delivered with ventilation, sump pump, ladder, and large access doors to avoid confined space restrictions. Once suspended solids are removed, Wahaso’s filtration and sanitation skid was designed to further sanitize the water as well as to minimize maintenance of the system. Special high-intensity UV units are utilized in the system to eliminate any potentially harmful pathogens, even if the water is cloudy. To minimize maintenance requirements, a special 50-micron filter was installed that is capable of self-cleaning while it is operating, eliminating the need to replace bag filters.


Wahaso’s stormwater harvesting system was installed and started up in time to join in the opening celebration of the Luther Ely Smith Square in the Fall of 2015. In the following Spring of 2016, harvested water was available and provided for irrigation of the lawns and landscaping.

The use of a below-grade water storage system and equipment room provides that the park will remain clear of obstructions so that attendees can focus on the beautiful Gateway Arch and surrounding park.