23 % of U.S.home mortgages are under water

The proportion of U.S. homeowners who owe more on their mortgages than the properties are worth has swelled to about 23%, threatening prospects for a sustained housing recovery.

Nearly 10.7 million households had negative equity in their homes in the third quarter, according to First American CoreLogic, a real-estate information company based in Santa Ana, Calif.

These so-called underwater mortgages pose a roadblock to a housing recovery because the properties are more likely to fall into bank foreclosure and get dumped into an already saturated market. Economists from J.P. Morgan Chase & Co. said Monday they didn't expect U.S. home prices to hit bottom until early 2011, citing the prospect of oversupply.

Home prices have fallen so far that 5.3 million U.S. households are tied to mortgages that are at least 20% higher than their home's value, the First American report said. More than 520,000 of these borrowers have received a notice of default, according to First American.

Most U.S. homeowners still have some equity, and nearly 24 million owner-occupied homes don't have any mortgage, according to the Census Bureau.