How safe is your tap water?

A chemical spill that leaked into a river in Charleston, W.Va. last week, poisoning the water supply for hundreds of thousands of people, has shed light on a problem that is much bigger than just the one incident.

An expert tells CBS News' Sharyl Attkisson that most big-city water treatment plants in this country are downstream from industrial facilities, and are vulnerable to contamination. Eric Olson with the Natural Resources Defense Council says it is a known problem, but so far the federal government is not stepping in to address it.

"There was an effort several years ago to try to protect drinking water supplies," he says, "so we didn't have this vulnerability to huge spills upstream. Unfortunately that died and never saw the light of day."

 Many communities, like Charleston, rely heavily on the chemical industry and other industrial manufacturers for jobs. Olson says that contributes to the reluctance to better regulate the industry.

"I think there certainly are politics involved here, and there are very powerful interests in the chemical and other industries that would rather not see strong regulatory requirements," he said.

In West Virginia, they are taking another look. The state head of environmental protection, Randy Huffman, said in a news conference Monday that they are looking into making some changes. "At the governor's request, (we are) developing some proposals for how we might more properly regulate these facilities in order to minimize the risk of a spill," Huffman said.

About 200,000 people still cannot use their water in the Charleston area. The system slowly started coming back online Monday, with customers instructed to wait until their "zone" was called -- something they could track on a website. As each zone comes back, customers must flush their pipes for about 20 minutes before they can start using the water.