By now, you’ve probably been strongly warned against drinking the water on an airline. Instead, it’s advised that travelers drink bottled water instead.

A recent study conducted by the Airline Water Study ranked the quality of 11 major and 12 regional airlines. They based their rankings on 10 criteria, including fleet size, ADWR violations, positive E. coli and coliform water sample reports and cooperation in providing answers to water-quality questions. An airline with a score of 3.0 or higher meant the water quality was relatively safe.

See how some of your favorite major airlines ranked below:

  • Alaska Airlines: 3.3
  • Allegiant Air: 3.3
  • Hawaiian Airlines: 3.1
  • Frontier Airlines: 2.6
  • Southwest Airlines: 2.4
  • Delta Air Lines: 1.6
  • American Airlines: 1.5
  • United Airlines: 1.2
  • JetBlue: 1
  • Spirit Airlines: 1

Regional airline rankings:

  • Piedmont Airlines: 4.33
  • Sun Country Airlines: 2.78
  • Envoy Air: 2.11
  • GoJet Airlines: 2
  • Trans States Airlines: 1.78
  • Compass Airlines 1.22
  • PSA Airlines: 1.22
  • SkyWest Airlines 1.11
  • Endeavor Air: 0.78
  • Air Wisconsin Airlines: 0.68
  • ExpressJet Airlines: 0.56
  • Republic Airways: 0.44

Want to protect yourself while in the friendly skies? Experts say that you should NEVER drink any water onboard that isn’t sealed in a bottled. Also, you shouldn’t drink coffee or tea onboard. Experts also do not recommend washing your hands after using the lavatories. Instead, they suggest bringing hand-sanitizer and using it as an alternative.