GCSD obtains the majority of its water from the San Francisco Public Utilities Commission’s (SFPUC) Hetch Hetchy Reservoir supply by pumping from a deep conveyance tunnel southeast of town, known as the Mountain Tunnel. The water originates in Yosemite National Park as snow melt from a large pristine watershed in the High Sierra. With controlled human contact and granite-type geology, the mineral content of this water is lower than most bottled water, and the bacterial counts approach zero. Because of the high quality of our source water, the District obtained a Filtration Avoidance permit (no filtration process required) on April 22, 1998, and during 2007 and 2008 began using disinfection-by-chloramination and ultraviolet disinfection to kill any pathogens, including Cryptosporidium and Giardia, that may be present in its surface water supply.