Stormwater Capture to Augment Water Supplies in the San Francisco Bay Area: Challenges, Opportunities, and Next Steps

This report provides a summary and synthesis of the Bay Area One Water Network’s workshop on stormwater capture to augment water supplies in the San Francisco Bay Area, held July 25-26, 2019 in San Francisco. The workshop brought together professionals in organizations responsible for stormwater management, water supply and wastewater treatment along with professionals from regulatory agencies, non-profits, and academia to discuss the potential of stormwater capture as a water supply option in the Bay Area.

With the prospect of urban water scarcity in California’s future, Bay Area water managers are seeking solutions to enhance the security of their water supplies. Stormwater is a locally available water source that could help diversify the region’s water supply portfolio. Stormwater capture in the Bay Area is challenging because much of the region’s geology is not conducive to infiltration of stormwater into groundwater aquifers. Nonetheless, stormwater capture is attractive because it can be cost-competitive with other new water supply options, it can reduce adverse effects of stormwater on local waterways and it can provide additional benefits like urban greening, wildlife habitat and flood prevention. The State of California is actively promoting stormwater capture, and it may be possible to leverage both existing infrastructure (i.e., for flood control) and existing funding opportunities to support stormwater capture projects.

Workshop participants considered four opportunities for stormwater capture in the Bay Area: 1. Large-scale stormwater capture and diversion to a place where it could be infiltrated to groundwater or stored in a reservoir; 2. Neighborhood-scale stormwater capture (i.e., at parks and ballfields) as part of green infrastructure projects; 3. Diversion of stormwater to wastewater treatment plants for reuse; and, 4. Household-scale cisterns and rainwater capture projects.

Each of these types of stormwater capture may play a role in the region’s future water supply portfolio. Regional coordination can ensure that stormwater capture projects are equitably distributed, cost-effective, and maximize multiple benefits.