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No Rain, No Gain: The Benefits and Opportunities of Urban Rainwater Harvesting in San Francisco

Undergraduate Practicum - Spring 2019
Charlie Beall, Michael Carter, Bridgette Guzman, Maddie McConkey, and Luke Miller
2019

As the third largest municipal utility in California, the San Francisco Public Utilities Commission
(SFPUC) has become a leader for innovative water management and conservation practices on
the West Coast. In a state like California, where droughts are recurring events, the SFPUC has
made it a priority to implement multiple water management methods in order to optimize the use
of finite water resources and ensure greater water resiliency and sustainability. San Francisco’s
combined sewer system, unique among West Coast cities, demands greater oversight and strict
pre-sewer storm water management to prevent sewage overflows during storm events. To
advance this aim, the SFPUC has specifically implemented a Storm water Management
Ordinance (SMO), requiring many new developments to reduce their storm water runoff rate
compared to pre-development conditions. Simultaneously, the SFPUC has implemented
guidelines for on-site rainwater harvesting and reuse (RWH), encouraging developers to
substitute collected rainwater for potable water to meet their non-potable demand. In
collaboration with the SFPUC, our team has produced a quantitative and qualitative analysis of
the city’s active and proposed storm water management projects, considering not only their
reductions of storm water flow to the sewer but also their success in using the rainwater and
storm water to help supplement on-site non-potable demands. This study focuses on the
implementation of RWH systems as a developer-chosen means to help achieve SMO
compliance; where the studied RWH system is typically in combination with a suite of other
plant-based or infiltration-based storm water Best Management Practices (BMP).