You've probably never given much thought to the quality of the water on an airplane.
Maybe it's time you should.
A recent study ranks the water served on major and regional US airlines.
Drink up if you're on an Alaska Airlines or Allegiant Air flight. Those two airlines tied for first place in the rankings in the study, from the Hunter College New York City Food Policy Center at the City University of New York and the website DietDetective.com.
But you might need to exercise some caution if you're on a JetBlue or Spirit flight. They tied for last among major airlines in the study, which came out at the end of August.
CNN reached out to Spirit and JetBlue for comment on their low rankings and is waiting to hear back.
The study was not a review of the bottled water that's often served in airplanes, but instead a look at the water used to make items like tea and coffee, as well as the water used in the bathrooms.
What should you do?
A list of recommendations for air travelers from the study include warnings not to drink water onboard an aircraft unless it is in a sealed bottle or to drink any coffee or tea prepared on board.
And instead of washing hands in the airplane's bathroom, the study encourages passengers to use hand sanitizer.
Airlines are required to provide safe drinking water for passengers and crew because of the Aircraft Drinking Water Rule, a federal government policy which dates back to 2011.
The airlines were given "water health scores" ranging from a 5 (the highest score) to a 0 (the lowest).
"A score of 3.0 or better indicates that the airline has relatively safe, clean water," the study says.
The criteria for the study included fleet size, the number of Aircraft Drinking Water Rule violations, results of water sample reports and how cooperative the airlines were in providing answers to questions about water quality.
Here are the rankings
The major airlines, and their rankings are:
Alaska Airlines, 3.3
Allegiant Air, 3.3
Hawaiian Airlines, 3.1
Frontier Airlines, 2.6
Southwest Airlines, 2.4
Delta Air Lines, 1.6
American Airlines, 1.5
United Airlines, 1.2
Spirit Airlines, 1