The water on some airplanes is unsafe — even for washing your hands — according to the results of the 2019 Airline Water Study from DietDetective.com and the Hunter College NYC Food Policy Center.

The 2011 federal Aircraft Drinking Water Rule requires airlines to provide crew and passengers with safe drinking water, but the study found the Environmental Protection Agency (one of the federal agencies responsible for enforcing the rule) rarely assesses penalties on airlines in violation of the ADWR.

The study looked at water given to passengers on 23 airlines, including 10 major and 13 regional. Each was issued a water health score between 5 and 0, based upon factors like coliform bacteria sampling reports, testing positive for E. coli, fleet size and the carrier’s cooperativeness in answering water-quality related questions. A score of 3 or higher indicates the airline supplies relatively clean, safe water.

Alaska Airlines and Allegiant tied for best water, with each scoring a 3.3/5. Hawaiian Airlines finished second at 3.1. Spirit and JetBlue came in last, tying with the lowest score of 1. Others included Frontier Airlines: 2.6; Southwest Airlines: 2.4; Delta Air Lines: 1.6; American Airlines: 1.5; and United Airlines: 1.2.

Among regional airlines, Piedmont Airlines, which operates American Eagle flights, is the highest-rated, with a score of 4.33. But beyond them, other regional carriers did poorly. Republic Airways, which operates United Express, Delta Connection and American Eagle flights, earned the lowest ranking at 0.44. ExpressJet had the second-worst score of 0.56.

The study recommends passengers avoid drinking onboard water that isn’t from a sealed bottle, and avoid coffee and tea. They also say you should use hand sanitizer rather than washing hands in the lavatory.