A new study released Wednesday shows that one in five U.S. homeowners with mortgages owe more than their properties are worth, and the figure in expected to increase as house values sink further. First American Corelogic found that about 8.31 million properties had negative equity at the end of 2008, up 9 percent from 7.63 million at the end of September. The percentage of so-called “underwater” borrowers rose to 20 percent from 18 percent. The study predicts that a further 2.16 million properties could go “underwater” if home prices fall another 5 percent. Forty-three U.S. states and Washington, D.C., were included in the study. Arizona, California, Florida, Georgia, Michigan, Nevada and Ohio remained the worst affected state housing markets, accounting for 62 percent of underwater borrowers and just 41 percent of mortgages. But the study showed other areas are increasingly facing similar pressure, with Connecticut seeing a 25 percent increase in homes with negative equity and Washington, D.C. showing a 44 percent increase. Roughly 68 percent of U.S. adults own their own homes, and about two-thirds of these have mortgages.