SAN FRANCISCO—Starting in March, San Francisco drinking water from Hetch Hetchy Reservoir will start being mixed with local groundwater.

Groundwater collects in aquifers, which are bodies of porous rock that can be tapped. In March, the city will begin to pump water from the Westside Groundwater Basin, which extends to approximately 400 feet below San Francisco. On March 10, 2015, the San Francisco Public Utilities Commission (SFPUC) adopted a resolution to include groundwater in the city’s drinking supply in order to diversify the city’s water supplies.

“Adding groundwater to our regional water supplies makes San Francisco’s water supply more reliable, particularly in the event of droughts and emergencies,” SFPUC stated on their website.

By 2020, 4 million gallons of water per day will be pumped from the Westside Groundwater Basin to the city of San Francisco.

San Francisco uses approximately 65 million gallons of water a day. The blend of water will never include more than 15 percent groundwater, and will start with just 3 percent this year.

When food critics from the San Francisco Chronicle sampled the new blend, they declared the difference in taste to be small. 

“It’s more distinctive in a good way,” said taster and former Chronicle wine critic Jon Bonne. “It tastes like what you want spring water to taste like.”

Locals of San Francisco have long used unadulterated drinking water, fresh from the Hetch Hetchy Reservoir in Yosemite National Park, 167 miles away. Since the 1930s, San Francisco has been supplied with snow melt filtered over the Sierra Nevada’s granite slopes. The water from Hetch Hetchy is treated, but not filtered because it is of such high quality.

San Francisco residents will be joining the majority of Californians who already drink groundwater. About 80 percent of Californians currently rely on some proportion groundwater to meet their daily needs.

For more information on the city’s initiative, visit this SFPUC site.