I have my own spin to put on the news that sales of existing homes plunged 27 percent in July: Stop thinking of your home as your cash cow.

In the last several decades, borrowers have heavily leveraged themselves using their houses to buy the things they’ve wanted – cars, vacations, college educations, better kitchens.

That’s one of the advantages of having a mortgage for a home. You can still use the home as collateral to borrow more money.

But an estimated one in seven homeowners now has a home worth less than what is owe on their mortgages and nearly 5 million need their home prices to rebound by 25 percent before they are back above water, according to a report on the “State of the Nation’s Housing” released earlier this summer by the Joint Center for Housing Studies of Harvard University.

With the rise in foreclosures and the decline in housing sales, we should be recalculating how homeownership fits into our net worth and how we view homeownership.

Housing wealth represents a large component of total family wealth, according to the most recent data compiled in the Federal Reserve’s Survey of Consumer Finances. In 2007, the primary residence accounted for 31.8 percent of total family assets.

You calculate your net worth (or wealth) by adding up the value of all your assets and then deducting all your liabilities. With a house, you deduct the amount you owe on your mortgage (liability) from the approximate fair-market value of the property. By the strict definition of net worth, if your home’s estimated market value is more than what you owe the bank, then you have equity, and that equity is considered an asset.

If you have a mortgage, home equity loan or line of credit on your home, you are not really a homeowner.

As many people discovered when the economy slammed into the Great Recession, if you lose your job and you no longer can pay your mortgage, you quickly realize you don’t own the property you so proudly proclaim is yours.

The National Association of Realtors’ report on home sales is alarming. Seasonally adjusted existing-home sales are at the lowest level since the association began collecting such data in 1999. Single-family sales are at the lowest level since May 1995.

“Given that home values are back in line relative to income … there is not likely to be any measurable change in home prices going forward,” said Lawrence Yun, the NAR’s chief economist, in releasing the July figures.

When the housing market improves, we need to resist going back to our old way of playing down a home as a liability. The latest home sales figures are further evidence the so-called equity in your home isn’t a sure thing on your personal balance sheet.