Study finds contaminants in California public-water supplies

SAN FRANCISCO Nearly one-fifth of the raw groundwater used for public drinking water systems in California contains excessive levels of potentially toxic contaminants, according to a decade-long U.S. Geological Survey study that provides one of the first comprehensive looks at the health of California’s public water supply and groundwater.

One of the surprises in the study of 11,000 public supply wells statewide is the extent to which high levels of arsenic, uranium and other naturally occurring but worrisome trace elements is present, authors of the study said.

Public-water systems are required to bring many contaminants down to acceptable levels before supplying customers. But the findings highlight potential concerns involving the more than 250,000 private wells where water quality is the responsibility of individual homeowners, state officials said.