Airplane tap water is not reliably safe to drink. The water stored onboard comes from a single tank that feeds both the lavatories and the galley, and testing consistently finds bacterial contamination at rates that would be unacceptable in a municipal water system. A recent study of more than 35,000 water samples from U.S. airlines found that 1.77% of samples from major carriers and 4.52% from regional carriers tested positive for E. coli.
Where Airplane Water Comes From
Every aircraft carries a potable water tank that supplies water to the lavatories and the galleys. The same tank that fills the bathroom sink also provides water for the coffee and tea makers. Water is loaded into the tank at the gate from airport water service vehicles, which connect to the local municipal supply. From that point forward, the water sits in an onboard storage tank until it’s used or the tank is drained and refilled.
The tanks themselves are the problem. They’re difficult to clean thoroughly, and between flushes they can develop biofilms, thin layers of bacteria that cling to interior surfaces and resist standard disinfection. The most common disinfectant is chlorine, and airlines are expected to maintain a residual chlorine level between 0.2 and 5 milligrams per liter. But maintaining that residual over hours of flight time, across dozens of fill cycles between deep cleans, is inconsistent in practice.
What Testing Has Found
A microbiological study published in the journal Environmental Science analyzed 154 water samples collected from aircraft and found 37 different bacterial species. Water from long-haul flights was significantly worse than water from short-haul flights, likely because the water sat in the tank longer and at varying temperatures. Among the bacteria identified were several species associated with hospital-acquired infections, including ones linked to bloodstream infections and respiratory illness. These are opportunistic pathogens, meaning they primarily pose a risk to people with weakened immune systems, but their presence signals that the water is far from clean.
The EPA’s Aircraft Drinking Water Rule requires airlines to test for coliform bacteria, a standard indicator of fecal contamination. Testing frequency depends on how often the airline disinfects and flushes its tanks, ranging from monthly sampling for airlines that flush 12 times a year down to annual sampling for those that flush once a year or less. If a sample tests positive for E. coli, the airline must restrict public access to the water system and disinfect and flush the entire system before follow-up testing. If a sample tests positive for total coliform but not E. coli, the airline can choose between disinfecting, restricting access, or simply retesting.
How Airlines Score on Water Safety
A 2026 study covering three years of data (October 2022 through September 2025) ranked 10 major and 11 regional U.S. airlines on a water safety scale from 0 to 5, factoring in E. coli violations, contamination rates, public notices, and disinfection frequency. A score of 3.5 or higher earned a passing grade. Here’s how the major carriers ranked:
- 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: 1.80 (Grade D)
- American Airlines: 1.75 (Grade D)
Regional carriers fared worse overall. Mesa Airlines scored 1.35, the only airline to receive a failing grade. GoJet Airlines was the only regional carrier to earn a B. The pattern is clear: water quality varies dramatically depending on who you fly with.
Are Coffee and Tea Any Safer?
Coffee and tea made onboard use the same tank water, but brewing temperatures typically exceed 190°F, which is hot enough to kill most bacteria. That makes hot beverages a somewhat safer bet than drinking the water straight from the tap. “Somewhat” is the key word. Brewing temperature doesn’t eliminate chemical contaminants or toxins that bacteria may have already produced in the tank, and it doesn’t address the cleanliness of the brewing equipment itself, which is also flushed with tank water between uses.
If you’re cautious about water quality, hot drinks are a step up from cold tap water but still not equivalent to water from a sealed bottle.
Who Should Be Most Careful
The CDC advises that infants, young children, pregnant women, older adults, and immunocompromised people are especially susceptible to illness from contaminated water. Their general guidance for travelers applies to aircraft as well: treat food and water served on flights with the same caution you’d apply to a restaurant. For anyone in a higher-risk category, sticking to bottled water or sealed canned beverages is the simplest way to avoid exposure.
Practical Steps to Protect Yourself
The safest approach is straightforward. Bring your own water bottle and fill it at an airport water fountain or buy a sealed bottle before boarding. Avoid drinking from the lavatory tap entirely. If you want coffee or tea, the boiling process reduces bacterial risk, but it doesn’t eliminate it completely.
You can also check your airline’s water safety score before flying. The difference between a Grade A airline and a Grade D airline is significant, and if you’re a frequent flyer, that exposure adds up. For most healthy adults, a single cup of airplane coffee is unlikely to cause illness. But making a habit of drinking onboard tap water, especially on long-haul flights where contamination rates are higher, increases your odds of encountering something unpleasant.