Rainstorms can lead to flooding that causes extensive damage to homes. Some families learn too late that flood damage isn't covered by traditional homeowners' policies.

There is a way families can protect their houses and furnishings. Since 1968, the federal government has sponsored the National Flood Insurance Program to make coverage available not only in high-risk zones but also in areas that are only occasionally threatened.

The program is overseen by the Federal Emergency Management Agency, or FEMA, with policies available to homeowners in more than 20,000 communities that have adopted flood plain management ordinances. The government sets the rates on the policies, which are available through insurance companies.

The two types of disasters not covered in standard homeowners' policies are floods and earthquakes, said Jeanne M. Salvatore, vice president for consumers affairs at the Insurance Information Institute, an educational center sponsored by property and casualty insurers.

"When it comes to water damage, one way to think about it is that homeowners insurance covers water from the top down, while flood insurance covers it from the bottom up," she said.

That is, if wind damages a roof and water pours in and ruins furniture and carpeting, a homeowners' policy generally will cover the repair or replacement costs. But if a nearby creek overflows and fills the house with a foot of mud and water, a family is out of luck unless it carries flood insurance.

According to FEMA, a homeowner is eligible for up to $250,000 coverage for the house and up to $100,000 for its contents. Renters can get coverage of up to $100,000 for furnishings. Some 4.6 million policies were in force last year, and more than $605 million in claims were paid, the agency said.

Coverage varies by how flood-prone an area is. The average premium is $520 a year for $100,000 worth of property coverage for a home without a basement and $615 per year for a home with a basement, FEMA estimates.

Insurance agent George Yates of East Hampton, N.Y., said eligible households should consider getting coverage. "You especially need it if you're in a high-hazard flood zone — low-lying areas, coastal areas, areas near rivers and streams," he said. "But even in zones where there's low probability, there can be flooding. In fact, about 20 percent of claims are from areas where you wouldn't expect to have a flood."