The study results showed that only one airline received the highest quality score.
Researchers from the Center for Food as Medicine and Longevity analyzed data on water quality aboard airplanes, collected by the Environmental Protection Agency (EPA). Some airlines showed good results: the water remained clean and did not contain potentially harmful bacteria such as Escherichia coli. However, many other companies had water quality ranging from average to extremely poor. Scientists note that the EPA could more effectively perform its functions, including imposing sanctions on airlines that regularly violate regulations.
In 2011, the EPA introduced the Aircraft Drinking Water Rule (ADWR), aimed at modernizing the onboard water supply system and improving its quality. Water in airplanes is typically stored in tanks for both domestic and international flights. According to these rules, airlines are required to regularly test the water for certain microorganisms.
Among them are coliform bacteria, which can cause illness and serve as an indicator of the presence of other microbes found in human feces. Tests also detect Escherichia coli (E. coli), a type of coliform bacteria that often causes food poisoning.
The Center's study on water quality in airlines covered 10 major and 11 regional airlines in the United States. Scientists analyzed EPA data collected from October 1, 2022, to September 30, 2025. A rating scale from 0 to 5 (with letter grades) was used to rank the airlines, based on several indicators: the total number of violations per aircraft, public notifications, exceedances of the allowable level of E. coli, and the frequency of water system cleaning.
The results showed that only one airline received the highest score of 5.0 – Delta Airlines. Frontier Airlines was the only other company with an A rating and a score of 4.80, while Alaska Airlines ranked third with a B rating (3.85). Among major airlines, American Airlines had the worst performance with a D rating (1.75). Almost all regional airlines scored low, with only GoJet Airlines receiving a B rating.
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