The San Francisco Public Utilities Commission (SFPUC) is advancing a series of major capital projects aimed at ensuring the reliability and resilience of its water and wastewater services for the city and surrounding region well into the next century.
At the centre of these efforts is the Mountain Tunnel Improvement Project, a rehabilitation of the 19-mile tunnel that forms a critical link in the Hetch Hetchy Regional Water System, which supplies drinking water to 2.7 million people across four Bay Area counties. Around 85% of the water the SFPUC delivers originates at Hetch Hetchy Reservoir in Yosemite National Park, and all of it must pass through this corridor. The two powerhouses flanking the tunnel, Kirkwood upstream and Moccasin downstream, generate 100% greenhouse gas-free hydroelectric power, with water moving entirely by gravity.
After nearly a century of continuous operation, portions of the tunnel required substantial repair. Works have included lining rehabilitation, improved maintenance access, and the construction of a new flow control valve facility designed to give operators greater control over water volumes moving through the system. The improvements are intended to protect water quality, optimise flow, and extend the tunnel's operational life by another hundred years. Because the tunnel must be drained and taken out of service for crews to work inside, construction is being carried out during winter shutdowns when demand is at its lowest. Works began in January 2021 and completion is scheduled for January 2027.
On the wastewater side, the West SoMa, Panhandle and Inner Sunset Large Sewer Improvements Project has been rehabilitating century-old sewer mains and laterals across several San Francisco neighbourhoods since October 2025. The work primarily relies on cured-in-place pipe rehabilitation, a trenchless method that allows crews to renew ageing infrastructure while limiting disruption to city streets and keeping sewer service running throughout construction. Where necessary, open-trench excavation is also carried out. The project is expected to wrap up in autumn 2026.
