Sioux City, Iowa, television station KCAU reports that the boil order was issued after testing of the city’s water revealed E. coli contamination.

Officials say tap water should be boiled for at least a minute before using it for drinking, brushing teeth, food preparation, washing dishes and making ice.

Residents will be informed when tests show no more contamination.

E. coli, a bacteria found in fecal matter, can be particularly dangerous to infants, young children, the elderly and those with compromised immune systems.