ALAMOSA, Colo. — Some residents in northern Alamosa were allowed to start using tap water for brief showers Saturday as crews continued a multiday flush of the city water system to purge salmonella bacteria.

The flush of about 50 miles of waterlines was being conducted in sections. In much of Alamosa, residents were still unable to use city water for anything but flushing toilets Saturday since high concentrations of chlorine were being used to flush the system.

On March 19, after several reported cases of salmonella and tests that showed bacteria in the water, state health officials warned residents not to use water straight from the tap for brushing teeth, washing dishes, drinking and cooking.

The disinfection of the city water system began earlier this week after officials confirmed the presence of salmonella in the water. The source of contamination is unknown.

As of Saturday, 315 people had become ill, with 85 cases of salmonella confirmed, the city said. Twelve of those people had cases requiring hospitalization.

The Comfort Inn, which uses well water instead of the city system, has been offering free showers since Thursday to residents and has served about 900 people, the city said.

The city and state have worked to distribute nearly 74,000 gallons of safe drinking water in the last week, the city said.

Salmonella can cause diarrhea, fever and stomach pain.