It's best not to drink water on airplanes: it can be hazardous to your health.

New research A study showed that the quality of drinking water on board US aircraft varies significantly depending on the airline. Many carriers, in violation of federal regulations, continue to provide passengers with potentially unsafe water.

The Center for Food as Medicine and Longevity published the 2026 Airline Water Study. It found that the quality of drinking water on board airplanes varies significantly. airlines continues to supply water that may be harmful to health.

Unsafe water violates the federal Aircraft Drinking Water Rule. It has been in effect since 2011 and requires airlines to provide passengers and crew with safe drinking water.

How was the study

The study assessed:

• 10 major airlines;
• 11 regional airlines.

The analysis period was three years – from October 1, 2022 to September 30, 2025.

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Each airline was assigned a "Water Safety Rating" on a scale from 0.00 to 5.00, with 5.00 being the highest. The rating was calculated using five weighted criteria, including:

• number of violations per aircraft;
• exceeding the permissible level of contaminants, including E. coli;
• the proportion of positive tests for indicator bacteria;
• availability of public notices;
• frequency of disinfection and flushing of systems.

A rating of 3.5 or higher indicates relatively clean and safe water and corresponds to a rating of A or B. The authors emphasized that the rating reflects the level of compliance and monitoring.

It does not guarantee the quality of water on a particular flight.

Best Airlines for Water Quality

The highest ratings among major airlines were received by:

• Delta Air Lines - 5.00, grade A;
• Frontier Airlines - 4.80, grade A;
• Alaska Airlines - 3.85, B rating.

Among regional carriers, GoJet Airlines took the lead with a score of 3.85 and a rating of B.

"Delta Air Lines and Frontier Airlines took the top spots for safest water in the sky, while Alaska Airlines came in third," said Charles Platkin, director of the Center for Food as Medicine and Longevity.

The worst results of the study

The worst performers among major airlines were:

• American Airlines - 1.75, D rating;
• JetBlue - 1.80, D rating.

Almost all regional airlines received low ratings. The weakest performers were:

• Mesa Airlines - 1.35, F rating;
• CommuteAir - 1.60, D rating.

CommuteAir had a particularly alarming result: 33.33% of water samples tested positive for total coliform bacteria.

Water safety ratings

Major airlines:

1. Delta Air Lines — 5.00, A.
2. Frontier Airlines - 4.80, A.
3. Alaska Airlines — 3.85, B.
4. Allegiant Air — 3.65, B.
5. Southwest Airlines - 3.30, C.
6. Hawaiian Airlines - 3.15, C.
7. United Airlines — 2.70, C.
8. Spirit Airlines — 2.05, D.
9. JetBlue — 1.80, D.
10. American Airlines - 1.75, D.

Regional Airlines Ranking:

1. GoJet Airlines — 3.85, B.
2. Piedmont Airlines - 3.05, C.
3. Sun Country Airlines - 3.00, C.
4. Endeavor Air — 2.95, C.
5. SkyWest Airlines — 2.40, D.
6. Envoy Air — 2.30, D.
7. PSA Airlines — 2.25, D.
8. Air Wisconsin Airlines - 2.15, D.
9. Republic Airways — 2.05, D.
10. CommuteAir — 1.60, D.
11. Mesa Airlines — 1.35, F.

What do federal regulations require?

The Aircraft Drinking Water Rule requires airlines to:

• Regularly collect water samples from tanks to test for coliform bacteria and possible presence of E. coli;
• disinfect and flush the tanks of each aircraft four times a year.

An alternative option allows for one disinfection per year, but then testing must be carried out monthly.

Where does the water on board come from?

Airplanes are refuelled with water at various airports, including those outside the United States. The quality of water on board also depends on the safety of the equipment used to supply it: water cabinets, tanks, carts, and hoses.

Unlike urban water systems with a constant flow and regular monitoring, aviation systems face different conditions:

• stagnation of water between flights;
• temperature changes during ascent and descent;
• mechanical loads during aircraft operation.

Such an environment can promote the formation of biofilms and the proliferation of microorganisms.

Recommendations for passengers

The Center for Food as Medicine and Longevity recommends that passengers take additional precautions:

• Never drink water on board unless it is in a sealed bottle;
• do not drink coffee or tea on the plane;
• Do not wash your hands with toilet water, but use hand sanitizer with at least 60% alcohol content.

Potential health risks

Drinking contaminated drinking water on board may result in:

• acute gastrointestinal diseases;
• contact with opportunistic microorganisms.

Those most at risk are:

• small children;
• elderly passengers;
• pregnant women;
• people with weakened immune systems.

For flight attendants, the situation is complicated by the fact that they regularly consume water on board as part of their work. Chronic exposure to even low levels of contaminants raises additional concerns.

Despite these risks, water quality on airplanes has historically received less regulatory and public attention than other aspects of aviation safety and food service.