Crews in Alamosa started pumping high concentrations of chlorine into the southern Colorado city’s water system Tuesday to rid it of salmonella bacteria that has sickened nearly 250 people.

Schools were closed because of the outbreak, and the Colorado National Guard and volunteers went door to door distributing red fliers notifying people not to use tap water for anything but flushing toilets.

City and state experts haven’t pinpointed the source of the contamination, but lab tests have confirmed that the water has made people ill.

Water distribution centers were set up throughout town, but residents were unsure they would be able to stay in their homes while the system was disinfected.

Mayor Pro Tem Kathy Rogers said there were plans to bring in temporary showers if necessary, but city officials hoped the water would be all right for bathing within a couple days.

It’s expected to be a couple weeks before people can drink the water. Neighboring communities, businesses and the National Guard have brought in bottled water and tankers

Salmonella is usually a food-borne disease and contamination of public water systems is rare. There were only 15 such cases between 1971 and 2004, according to the Centers for Disease Control and Prevention.

No fecal matter has been found in the water, ruling out cross contamination between drinking water and wastewater. Officials have also ruled out disgruntled employees and terrorism.

Alamosa Public Works Director Don Koskelin said the city has examined businesses such as car washes and other potential sources of contamination, but have found nothing. He said he believes this is a one-time event that will be solved by flushing more than 50 miles of water lines.

The total number of salmonella cases has jumped to 248, with 72 cases confirmed, said John Pape, an epidemiologist with the state health department.

Salmonella can cause diarrhea, fever and stomach pain. Victims typically recover on their own, but the elderly, infants and people with impaired immune systems may require treatment.

Untreated, salmonella can cause death in vulnerable victims, the health department said.

Alamosa’s water is drawn from a deep well that taps an aquifer, an underground water formation. The water is pumped directly to residents and businesses without any chlorination.

Before the salmonella outbreak, work had begun on a water treatment plant that is scheduled to open in June.