A new analysis released by the Center for Food as Medicine and Longevity has found variation in the quality of drinking water available to passengers and crews on commercial flights, with many airlines’ water falling below safety thresholds.
The 2026 Airline Water Study evaluated onboard water quality from 10 major carriers and 11 regional airlines using data from the federal Aircraft Drinking Water Rule (ADWR) covering October 1, 2022, through September 30, 2025. The ADWR, first implemented in 2011, requires airlines with onboard water systems to regularly sample water for contaminants, including E. coli and coliform bacteria, disinfect and flush tanks periodically, and take corrective action when problems are detected.
Each airline was assigned a “Water Safety Score” on a scale from 0.00 (lowest) to 5.00 (highest) based on five weighted indicators: violations per aircraft, Maximum Contaminant Level violations for E. coli, positive indicator rates for coliform, public notices issued when problems occur, and frequency of disinfecting and flushing. A score of 3.5 or above was designated as indicating relatively safe, clean water.
“Delta Air Lines and Frontier Airlines win the top spots with the safest water in the sky, and Alaska Airlines finishes No. 3,” said Charles Platkin, PhD, JD, MPH, director of the Center for Food as Medicine and Longevity.
According to the study, Delta Air Lines earned a perfect score of 5.00 (Grade A), followed closely by Frontier Airlines with 4.80 (Grade A). Alaska Airlines received a 3.85 (Grade B), placing it third among major carriers. Allegiant Air also scored in the “relatively safe” range with 3.65, while Southwest and Hawaiian Airlines scored 3.30 and 3.15, respectively (Grades C). United Airlines, Spirit Airlines, JetBlue, and American Airlines scored lower, with American posting the lowest major-carrier score of 1.75 (Grade D).
The study also highlighted the role of enforcement, finding that the Environmental Protection Agency (EPA) rarely levies civil penalties against airlines for violations of the rule
Regional carriers generally performed less well. GoJet Airlines was the highest-scoring regional airline with a 3.85 (Grade B) score. Others, such as Piedmont Airlines, Sun Country Airlines, and Endeavor Air, scored in the mid-range (Grades C), while several regional carriers, including Mesa Airlines (1.35, Grade F) and CommuteAir (1.60, Grade D), received low marks. The study noted that CommuteAir had a relatively high proportion of samples positive for total coliform.
“Nearly all regional airlines need to improve their onboard water safety, with the exception of GoJet Airlines,” Platkin said.
The analysis examined 35,674 sample locations across all carriers. Of those, 949 locations, about 2.66 %, tested positive for total coliform bacteria, which the study notes is an indicator that conditions could support disease-causing organisms. Maximum Contaminant Level violations for E. coli also contributed to lower scores for several airlines.
The study also highlighted the role of enforcement, finding that the Environmental Protection Agency (EPA), the agency responsible for ensuring compliance with the ADWR, rarely levies civil penalties against airlines for violations of the rule.
Aircraft water systems face unique challenges compared with municipal water supplies. Water is loaded onto aircraft at different airports, stored in tanks under variable temperature and pressure conditions, and distributed through complex plumbing, all of which can contribute to stagnation and microbial growth if maintenance is inadequate.
To inform passengers of potential risks, the Center offered several practical recommendations: “NEVER drink any water onboard that isn’t in a sealed bottle,” avoid coffee or tea made with onboard tap water, and use alcohol-based hand sanitizer containing at least 60 % alcohol instead of washing with tap water in airplane lavatories.
