SHAFTER, Calif. (AP) – The 17,000 residents of the San Joaquin Valley city of Shafter have been told to boil tap water or switch to bottled water after coliform was found in samples collected last week.

A statement posted on the city’s website Monday says the bacterium is not dangerous on its own, but can provide an indication of other types of contamination.

The city says boiled tap water or bottled water should be used for drinking, cooking, dish washing and washing hands before preparing food.

In addition, many restaurants, markets, food processing facilities and other businesses deemed to be sensitive to water quality issues must cease operations.

The city says it doesn’t have an estimate of when service will return to normal. In the meantime state authorities are inspecting the city water system.