Airline passengers may want to rethink what they drink on board. A new study has warned that water served on many flights could be potentially unhealthy, prompting researchers to advise travelers to stick to bottled water and avoid coffee or tea prepared using aircraft water systems. The findings come from the Center for Food as Medicine & Longevity, which analyzed more than 35,000 water samples collected from 10 major and 11 regional airlines over a three-year period. Based on the results, the nonprofit also recommends avoiding washing hands with airplane tap water and instead using hand sanitizer with at least 60% alcohol. While water quality may not rank high among passengers’ safety concerns, the organization described it as an important public health issue. Drinking contaminated aircraft water, it warned, can lead to gastrointestinal illness and potential exposure to harmful pathogens. What the study found The analysis showed that 2.7% of samples tested positive for total coliform bacteria, an indicator that disease-causing organisms may be present in the water system. More alarmingly, E. coli was detected 32 times across the 21 airlines reviewed. “Testing for coliform bacteria is critical because its presence suggests that pathogens could enter the drinking water supply,” the group said. In the United States, onboard water systems are regulated under the Environmental Protection Agency’s Aircraft Drinking Water Rule (ADWR), introduced in 2011. The rule requires airlines to regularly test water, flush and disinfect tanks multiple times a year, and monitor for contamination. However, the study noted that enforcement is inconsistent and penalties for violations are rarely imposed. Airlines respond Several airlines pushed back against the findings. American Airlines said it is reviewing the study but stressed that its potable water program complies fully with EPA rules and has passed recent audits without violations. JetBlue Airways said it follows EPA, FDA, and FAA standards and primarily serves bottled drinking water onboard.Spirit Airlines said it maintains a comprehensive testing and maintenance program and has improved procedures in recent years. Industry group Airlines for America said passenger and crew safety remains the sector’s top priority, adding that U.S. airlines follow federal guidelines to ensure onboard water safety. Major airlines ranked: best to worst The study scored airlines on a five-point scale, with points deducted for violations such as detecting contaminants in water samples. 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 Airways — 1.80 (Grade D) American Airlines — 1.75 (Grade D) Regional airlines ranked: best to worst 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 — 2.15 (Grade D) Republic Airways — 2.05 (Grade D) CommuteAir — 1.60 (Grade D) Mesa Airlines — 1.35 (Grade F) What passengers should do Until oversight improves, researchers advise travelers to avoid aircraft tap water entirely—including coffee and tea—and rely on sealed bottled beverages. For hygiene, alcohol-based hand sanitizer is considered safer than washing hands with onboard water. The study concludes that while many airlines meet basic regulatory requirements, stronger enforcement and greater transparency are needed to ensure that something as simple as a glass of water at 35,000 feet does not pose a health risk.