Just how clean is your drinking water? If you're like most Americans, you probably think that the water coming from your tap is chemical- and sediment-free and up to snuff with the latest federal standards and regulations.

But if you live in cities like Pensacola, Fla.; Riverside, Calif.; or Las Vegas, Nev., you may want to think again. Those cities are rated as having the worst drinking water in the U.S., based on a survey by the website 24/7 Wall St.

The website used data collected from multiple sources for five years (ending in 2009) by Environmental Working Group, a nonprofit eco-research and advocacy group based in Washington, D.C. 

Cities in Kansas, Louisiana, Mississippi, Tennessee and Georgia were not included in the EWG database because they provided insufficient data. A few major cities, namely, Detroit, Salt Lake City and Washington, D.C., also neglected to provide sufficient data.

Still, using the data that the EWG collected, 24/7 Wall St. came up with its 10 U.S. cities with the worst drinking water based on three qualifiers:

  • The percentage of chemicals found based on the number that were tested for
  • The total number of contaminants found
  • The most dangerous average level of a single pollutant
Without further ado, here are the 10 American cities with the worst drinking water, with the omissions noted above:

10. Jacksonville, Fla.

9. San Diego, Calif.

8. North Las Vegas, Nev.

7. Omaha, Neb.

6. Houston, Texas

5. Reno, Nev.

4. Riverside County, Calif.

3. Las Vegas, Nev.

2. Riverside, Calif.

1. Pensacola, Fla.

[via Daily Finance]