DIXON, Calif. -- A boiled water notice was issued Tuesday night for some residents of Dixon.

The California Water Service Co., a private utility, said a water sample collected on Sunday came back positive for E. coli.

The utility immediately notified the 300 affected households by going door to door after the results came back. The sample was taken from a water main repair site.

The main area affected is in the Country Faire subdivision and a small portion of the older part of downtown.

Residents are urged to boil water before use until further notice.

The source of contamination is unknown.

The utility is continuing to take samples.