If you order coffee or tea on a flight, you may want to think twice.

A 2026 airline water study found that drinking water quality can vary sharply from one airline to another, and that many carriers still fail to meet federal safety standards meant to protect passengers and crew.

The study — from the Center for Food as Medicine & Longevity — reviewed airline water testing data collected from Oct. 1, 2022, through Sept. 30, 2025. 

Researchers evaluated 10 major airlines and 11 regional carriers, giving each a Water Safety Score ranging from a low of 0.00 to a high of 5.00. A score of 3.5 or higher earned a Grade A or B, meaning relatively safe onboard water.

"Delta Air Lines and Frontier Airlines win the top spots with the safest water in the sky, and Alaska Airlines finishes No. 3," the center’s director, Charles Platkin, said in a news release.

By contrast, the lowest-scoring major airlines were American Airlines and JetBlue, the study found. 

"Nearly all regional airlines need to improve their onboard water safety, with the exception of GoJet Airlines," Platkin added.

The federal Aircraft Drinking Water Rule (ADWR), in place since 2011, requires airlines to provide safe drinking water onboard. 

Airlines must regularly test water tanks for coliform bacteria and possible E. coli, and they must disinfect and flush each aircraft’s water system multiple times per year.

To score airlines, researchers looked at five weighted factors, including:

• Violations per aircraft

• Maximum Contaminant Level violations for E. coli

• Rates of coliform-positive tests

• Public notices

• How often water systems were disinfected and flushed

Across all airlines studied, 35,674 water sample locations were tested for coliform bacteria. Of those, 949 samples (2.7%) tested positive.

The study also identified 32 E. coli violations across the 21 airlines analyzed, the single biggest factor dragging scores down.

Among the key findings:

• Delta Air Lines earned a perfect 5.00 (Grade A).

• Frontier Airlines scored 4.80 (Grade A).

• Alaska Airlines followed with 3.85 (Grade B).

• GoJet Airlines was the highest-rated regional carrier at 3.85 (Grade B).

• American Airlines ranked lowest among major airlines at 1.75 (Grade D).

• Mesa Airlines scored 1.35 (Grade F), the lowest among regional carriers.

• CommuteAir had a 33.33% coliform-positive rate, one of the highest in the study.

The report’s "Shame on You" award went to the U.S. Environmental Protection Agency (EPA), which shares responsibility for enforcing aircraft water safety standards. Civil penalties for airline water violations remain extremely rare, the study noted.

Testing for coliform bacteria matters because its presence can signal that disease-causing organisms may also be in the water system. 

When samples test positive, airlines are required to quickly retest, disinfect, flush or shut down affected systems, depending on results.

Because aircraft refill water tanks from many locations, including international airports, onboard water quality can also be affected by hoses, trucks and other transfer equipment, researchers noted.

Until airline water systems improve, the Center for Food as Medicine & Longevity offers clear guidance for travelers who want to reduce risk.

“NEVER drink any water onboard that isn’t in a sealed bottle,” the group advises.

They also recommend skipping onboard coffee and tea and using alcohol-based hand sanitizer with at least 60% alcohol instead of washing hands with airplane sink water.