This is from the SFO website

Hydration Stations
Refill, reuse and refresh at SFO’s new Hydration Stations. These innovative water bottle refill stations provide access to San Francisco’s free high-quality, great tasting tap water.

San Francisco tap water—pristine Sierra snowmelt that comes from the Hetch Hetchy reservoir located in Yosemite National Park and from within two protected local watersheds in the Bay Area—is some of the purest, safest and best tasting water in the world.

The Hydration Stations also encourage the conservation of our natural resources and preservation of our environment by helping to reduce the solid waste created from single-use plastic water bottles.

For more information about San Francisco’s water bottle refill program and San Francisco tap water, please visit the San Francisco Public Utilities Commission website.

SFO’s Hydration Stations are located post-security in all Boarding Areas.