­In November 2008, the Grand Forks Herald reported icy patches on the streets of Grand Forks, N.D. But it wasn't because of wintry precipitation: The problem came from sump-pump runoff meeting subfreezing temperatures [source: Grand Forks Herald]. But in spite of the trouble they caused for pedestrians and motorists, the sump pumps were doing an important job of their own -- keeping basement­s from flooding.

A sump pump is a small pump installed in the lowest part of a basement or crawlspace. Its job is to help keep the area under the building dry and to prevent it from flood­ing. Usually, sump pumps are installed in specially constructed sump pits. Water flows into the sump pit through drains or by natural water migration through the soil. The sump pump's job is to pump the water out of the pit and away from the building so the basement or crawlspace stays dry.

According to the American Society of Home Inspectors, more than 60 percent of American homes suffer from below-ground wetness [source: Basement Systems]. But even more homeowners are likely to have to deal with a flooded basement at some point. It doesn't take much water to cause thousands of dollars of damage. A moist basement can also lead to mold and mildew growth, bringing with it all its related health and breathing hazards.

­Sump pumps have been a common fixture in some homes for years, primarily in low-lying areas or places where r­apid melting of heavy snow can lead to flooded basements. However, legislation, including amendments to the U.S. Federal Clean Water Act in 1987, has made sump pumps a requirement in homes that aren't necessarily at a high risk for flooding. Today, sump pumps are common in new construction homes.

So how does a sump pump keep the water out -- and what do you do if it stops working? Read on to learn how to stay afloat when the water's high.