The report, ordered by the state Legislature, shows that from 2002 to 2010, 680 out of a little more than 3,000 community water systems in the state relied on one or more contaminated groundwater wells. Those contaminated wells served 21 million people.
Arsenic was the most-detected naturally occurring contaminant, while nitrate was the human-caused contaminant detected the most. Chemical fertilizers and livestock manure are the main source of nitrate contamination in groundwater.
The report stresses that most of the communities blend or treat their water with cleaner supplies, drill a new well or provide another alternative source, passing on the extra costs to rate payers. According to the California Department of Public Health, over 98 percent of Californians on public water supply are served safe drinking water.
But some communities cannot afford water treatment or other alternatives. The report said 265 community water systems have delivered water from wells that have exceeded the nitrate, arsenic or other standards. Most of these communities are located in rural Kern, Tulare and Madera counties and serve contaminated water to about 2 million Californians.