Recent flooding has prompted Austin city leaders to say immediate action is needed to keep the city from running out of water. "It's imperative that not only you boil water that you're going to consume, but you do all that you can to reduce the amount of water that you use until we can get through this event," Austin water director Greg Meszaros said.

The city's warning sent crowds of people scrambling to buy bottled water, stripping store shelves clean, reports CBS News correspondent David Begnaud.

"After seeing so many people, I thought I should probably get three cases," Austin resident Monica Marcano said.

Health officials say the tap water may contain bacteria and viruses that could make people sick.

"These organisms are extremely small and even potentially a droplet of water that is affected could be enough to cause an illness," Dr. Harry Thomas said.

Historic flooding has washed mud, silt, and other contaminants into the Colorado River and nearby lakes that supply Austin's water. In response, the city shut down portions of its three treatment plants for cleaning. Customers in Austin typically use some 120 million gallons of water daily.

"Normally, we could produce over 300 million gallons a day. We haven't been much over 100 for the last two days," Meszaros said.

The city's restaurants are among the hardest hit. Many owners have closed their doors until they can safely reopen.

"This is the first time, you know, in history that we have a problem like this. So we can't take it lightly," Yamil Hernandez of Morelia Mexican Grill said.

Officials say so far, no tests have returned positive for bacteria in the drinking water, but there is still a chance people could get sick. The CDC says most household water filters typically do not remove bacteria or viruses, and you should boil water for a minimum of three minutes to make it safe to drink.