Coastside County Water District has very low levels of naturally occurring fluoride in our source waters: 0.24 parts/million [ppm] in Denniston Reservoir, 0.32 ppm in the Denniston well field and 0.18 ppm in the Pilarcitos well field. The maximum contaminant level [mcl] is 2 ppm. Since the San Francisco Public Utilities Commission (SFPUC) initiated fluoridation in 2005, fluoride levels in Upper Crystal Springs Reservoir have risen from 0.2 ppm to 0.85 ppm.