Forbes has compiled a list of "America's 20 Dirtiest Cities" and there's the Philadelphia metropolitan area, ranked No. 3, behind Fresno and Bakersfield, two California areas with fewer than a million residents apiece.

But don't think "Philthadelphia," with trash-strewn streets or vacant lots - or foul-mouthed sports fans.

Pollution is Forbes' main focus. Air and water quality.

As with most such lists, the accuracy can be questioned.

Last year, when Philly finished first, the list was dubbed "Most Toxic," prompting the likes of fairwarning.com to suggest, "Americans seeking healthy cities to call home should avoid Philadelphia like a toxic waste dump."

Yet somehow tourists flock here, and, amazingly, it's tough to find a gas-mask cart on Independence Mall.

OK, we've all seen people lugging and chugging bottled water. But isn't that true everywhere?

Some reasons not to panic:

When it comes to toxic releases, Houston "leads by a mile," says Forbes.

Twenty-one areas have worse air than Philadelphia, according to Sperling's Best Places (www.bestplaces.com), a measure used by Forbes.

Last year, for generally healthy people, the Philadelphia area had ZERO unhealthy air-quality days, while, to check just two examples, Los Angeles had 11 and Fresno had 22, according to the EPA.

Forbes also used data for "watershed quality," not drinking water, which would seem to be more important to health. According to the city's latest drinking water report, "We have consistently performed better than all drinking water standards developed by the EPA to protect public health."

Besides, going the bottled or filtered route is much easier than trying not to breathe.

More meaningful might be statistics about how this supposed toxic exposure translates into illness.

But in terms of cancer incidence, the city of Philadelphia didn't finish in the top 10 percent of the nation's more than 3,000 counties, according to the National Cancer Institute.

Not that the region gets a clean bill of health.

Here are some county rankings, based on data for the years 2005 to 2009: Gloucester (148), Burlington (166) and Camden (185); Delaware (193) and Philadelphia (384) in Southeastern in Southeastern Pennsylvania; and New Castle County (476) in Delaware.

Bucks, Chester, Northampton, Mercer, Cape May, Atlantic and Salem Counties also appear in the top 30 percent.

Contact staff writer Peter Mucha at 215-854-4342 or pmucha@phillynews.com.