By now, most airline passengers already know that you shouldn't drink the water on airlines. Airplane water has long had a reputation for being germy and potentially a source of waterborne pathogens.
Think about that. You've known that airline water is iffy. You've known it for years. Seems like everyone knows.
So if the problem has been going on for years, why haven't regulators changed it?
That's just one of the questions asked by the Center for Food as Medicine and Longevity as part of its 2026 Airline Water Study, released a few weeks ago.
The latest study is another effort by consumer groups to see if federal rules are being enforced. After all, the federal government's Aircraft Drinking Water Rule (ADWR), which was put into place in 2011, requires airlines to provide passengers and flight crew with safe drinking water.
Airline water is notoriously dirty because it's so hard to keep clean. Water can arrive in aircraft tanks unclean or it can be contaminated by crew, hoses, or neglected equipment. It can experience wide fluctuations in temperature and sit stagnant for long periods in between flights, both of which "can create environments conducive to biofilm formation and microbial proliferation," the Center for Food as Medicine explains.
Regular disinfection and system flushing is required to keep airline water pure. But are airlines doing that?
Even though the 2011 ADWR has more lenient cleanliness standards than land-based drinking water systems, a 2019 study found that despite the rule, airline water was still often populated with enough bacteria to turn a petri dish into a party.
That 2019 study advised passengers to never drink any water on an airline that wasn't served in a sealed bottle. It also told passengers to steer clear of hot coffee and tea, which is made from water drawn from questionably clean plumbing.
Now it's 2026. So how dirty is airline water now?
What recent airline water tests found
The 2026 Airline Water Study ranked 10 major and 11 regional airlines by the quality of water they provided on flights during a three-year study period from October 1, 2022, to September 30, 2025.
According to the Center for Food as Medicine and Longevity, "Each airline was given a 'Water Safety Score' (5.00 = highest rating, 0.00 = lowest) based on five weighted criteria, including violations per aircraft, maximum contaminant Level violations for E. coli, indicator-positive rates, public notices, and disinfecting and flushing frequency. A score of 3.5 or better indicates that the airline has relatively safe, clean water and earns a Grade A or B."
E. coli, as you unfortunately probably know, is a bacteria that typically lives in the gut and is spread through fecal-oral transmission. That's one of the things scientists were looking for in airline water—and they found plenty.
When the final results came in, the warning for passengers was unchanged. Every time you drink a cup of coffee or sip a cup of water you run the risk of ingesting a zoo's worth of microorganisms.
From the study authors: "NEVER drink any water on board that isn’t in a sealed bottle. Do not drink coffee or tea on board. Do not wash your hands in the bathroom; use alcohol-based hand sanitizer containing at least 60% alcohol instead."
Which airlines have the dirtiest water
In tests, regional airlines tended to have nastier water than the mainline carriers: 4.52% of samples from regional carriers tested positive for E. coli, whereas 1.77% of major airlines tested positive.
Where airlines earned a low score, it was usually because of failing grades for E. Coli.
Of the majors, Delta Air Lines fared the best. But American Airlines crapped out at 1.75, at the bottom of all U.S. major carriers. JetBlue didn't do much better.
Major airlines' water scores
- Delta Air Lines: 5.00 (Grade A)
- Frontier Airlines: 4.80 (Grade A)
- Alaska Airlines: 3.85 (Grade B)
- Allegiant Air: 3.65 (Grade B)
- Southwest Airlines: 3.30 (Grade C)
- Hawaiian Airlines: 3.15 (Grade C)
- United Airlines: 2.70 (Grade C)
- Spirit Airlines: 2.05 (Grade D)
- JetBlue: 1.80 (Grade D)
- American Airlines: 1.75 (Grade D)
Regional airlines' water scores
- GoJet Airlines: 3.85 (Grade B)
- Piedmont Airlines: 3.05 (Grade C)
- Sun Country Airlines: 3.00 (Grade C)
- Endeavor Air: 2.95 (Grade C)
- SkyWest Airlines: 2.40 (Grade D)
- Envoy Air: 2.30 (Grade D)
- PSA Airlines: 2.25 (Grade D)
- Air Wisconsin Airlines: 2.15 (Grade D)
- Republic Airways: 2.05 (Grade D)
- CommuteAir: 1.60 (Grade D)
- Mesa Airlines: 1.35 (Grade F)
For the complete study results, including how many samples were collected from each airline to determine its score, see the website for The Center for Food as Medicine.
The study did not test ice cubes. Sometimes, airline ice is made in on-board icemakers, in which case the cubes would be a reflection of the drinking water they're filled with, and sometimes ice is delivered to aircraft by third-party services.
(But even sourcing ice offsite doesn't mean it'll be clean. As Travel + Leisure reported last fall, "a 2017 peer-reviewed study published in the Annals of Microbiology, researchers took samples from 60 ice cubes from both domestic and industrial facilities, which contained more than 50 different strains of bacteria.")
Which leads us back to the question that opened this discussion: If we all know airline water is unsafe and there is a 15-year-old federal rule that was supposed to make it safe, why isn't it safe by now? The airlines have had 15 years to respond to this.
The answer, of course, is exactly what we have come to expect: "The study shows that civil penalties for ADWR violations remain extremely rare if at all (we are not able to get an answer)," the Center's authors wrote.