A number of large population centers in California have developed
their own extensive water projects. The Hetch Hetchy Project
transports Tuolumne River water 156 miles from the Central Sierra
to San Francisco and peninsula cities.
The East Bay Municipal Utility District supplies cities on the
east side of San Francisco Bay with Mokelumne River water.
About 30 percent of California’s total annual water supply comes
from groundwater in normal years, and up to 60 percent in drought
years. Local communities’ usage may be different; many areas rely
exclusively on groundwater while others use only surface water
supplies. Contrary to popular opinion, groundwater does not exist
in underground lakes. Groundwater fills pores (spaces) between
sand, gravel, silt and clay in water-bearing formations known as