A three-year analysis of U.S. airline water quality has revealed a dramatic gap between carriers that keep their tanks clean and those that don’t.
At a Glance
- Delta and Frontier earned the only “A” grades for onboard water safety
- American Airlines scored a “D” and regional Mesa Airlines flunked with an “F”
- Researchers advise skipping coffee, tea and tap water in favor of sealed bottles
Passengers who routinely accept a free cup of water or mid-flight coffee may want to reconsider. A sweeping study released Dec. 29, 2025, shows that water quality aboard many planes falls short of safety standards.
Study Scope & Method
The Center for Food as Medicine and Longevity tested 35,674 water samples from 21 U.S. carriers between Oct. 1, 2022, and Sept. 30, 2025. Each airline received a 0-5 Water Safety Score; anything below 3.5 was flagged as potentially unhealthy.
Researchers weighed:
- Violations per aircraft
- E. coli Maximum Contaminant Level breaches
- Indicator-positive bacteria rates
- Public notices issued
- Disinfecting and flushing frequency
Best & Worst Performers
| Rank | Airline | Score | Grade |
|---|---|---|---|
| 1 | Delta Air Lines | 5.00 | A |
| 2 | Frontier Airlines | 4.80 | A |
| 3 | Alaska Airlines | 3.85 | B |
| 10 | American Airlines | 1.75 | D |
| 21 | Mesa Airlines | 1.35 | F |
GoJet Airlines was the only regional carrier to earn a “B,” while nearly every other regional scored in the “C” to “F” range.
Charles Platkin, PhD, JD, MPH, director of the Center, summarized:
> “Delta Air Lines and Frontier Airlines win the top spots with the safest water in the sky.”
Health Precautions for Flyers
The Center recommends travelers:
- Bring sealed bottled water instead of drinking tap
- Avoid coffee and tea brewed with tank water
- Skip hand-washing in lavatories; use ≥60 % alcohol sanitizer
- Fill reusable bottles at airport refill stations
- If tap use is unavoidable, let water run 30 s to flush stagnant supply
Key Takeaways
- Only two major U.S. airlines scored above 4.0 for water safety
- Regional carriers largely trail majors in water quality
- The 2011 Aircraft Drinking Water Rule still leaves enforcement gaps
- Simple passenger habits-sealed water, sanitizer-sharply cut exposure risk
Bottom line: the next time a flight attendant offers a complimentary drink, choosing bottled water could be the healthiest decision at 35,000 feet.
