Air passengers sometimes find themselves torn between advice to stay hydrated on flights and social media guidance from air stewards who claim the in-flight water is unclean. A new study now reveals that the air stewards could be right, and names and shames the US airlines with the worst water safety data. Some of the biggest US airlines have work to do on water safety, the research shows.
The Center for Food as Medicine and Longevity analysed water test results reported by airlines to the Environmental Protection Agency (EPA) over the three years between October 2022 and September 2025. In total, 35,674 water tests were conducted on samples taken from aircraft water sources such as taps in galleys and bathroom basins.
The scientists ranked 10 major carriers and 11 regional airlines by the quality of water they provided onboard flights, giving them a “Water Safety Score” (5.00 = highest rating, 0.00 = lowest) based on five 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,” the 2026 Airline Water Study said.
Airlines are legally required to disinfect and flush galleys and bathroom systems four times per year. But the study explained that “periods of stagnation between flights, temperature variations during ascent and descent, and mechanical stress from aircraft operations” can all create conditions in which bacteria thrive.
Among the majors, the “safest water in the sky” was found on Delta Air Lines and Frontier Airlines, with Alaska Airlines in third place, sharing a B grade with Allegiant. Hawaiian, Southwest, and United were graded C.
Meanwhile, the worst scores were on American Airlines and JetBlue. American scored just 1.75 out of five, or a grade D. JetBlue managed slightly better with a score of 1.8 but was still graded a D, and was ranked lowest in a 2019 water safety report, so it shows little improvement. Spirit also received a D grade.
Regional airlines fared even worse. Six regional carriers were graded D: CommuteAir, Envoy Air, PSA Airlines, Republic Airways, SkyWest Airlines, and Air Wisconsin. Mesa Airlines was awarded an F.
| Major Airlines | Water Grade |
| 1. Delta Airlines | 5.00 (A) |
| 2. Frontier Airlines | 4.80 (A) |
| 3. Alaska Airlines | 3.85 (B) |
| 4. Allegiant Air | 3.65 (B) |
| 5. Southwest Airlines | 3.30 (C) |
| 6. Hawaiian Airlines | 3.15 (C) |
| 7. United Airlines | 2.70 (C) |
| 8. Spirit Airlines | 2.05 (D) |
| 9. JetBlue | 1.80 (D) |
| 10. American Airlines | 1.75 (D) |
“Nearly all regional airlines need to improve their onboard water safety, with the exception of GoJet Airlines,” said Charles Platkin, Director of the Center for Food as Medicine and Longevity.
The water tests looked for so-called coliform bacteria and possible E. coli, which are signs of faecal pollution. Some strains can cause symptoms such as stomach pain and diarrhea, and other potentially fatal illnesses, including kidney disease. The “good news” for air passengers is that “only” 949, or 2.66% of the samples, tested positive for coliforms, and 32 (0.09%) tested positive for E. coli.
Still, many may think twice before drinking the coffee or filling a cup from the tap on a plane again—and Platkin would agree with that hesitation, advising: “Never drink any water onboard that isn’t in a sealed bottle and do not drink coffee or tea onboard.” He also warned against washing hands in bathrooms, recommending a 60% alcohol-based hand cleanser instead.
In a statement, American Airlines denied any violations and insisted its “potable water program is fully in compliance with the Environmental Protection Agency’s (EPA) Aircraft Drinking Water Rule (ADWR).”
