The fasten seatbelts light just went off and the flight attendant is offering you a drink. You know staying hydrated is important, so you consider your options. It’s safe to drink the water — or coffee or tea made with the water — on an airplane, right?

The answer, like the stuff coming out of the airplane bathroom tap, might be a little murky.

If you order water on a flight, chances are it’s coming out of a bottle — so you’re safe. But if you see the attendant pouring water out of a pitcher, choose a canned or bottled beverage instead.

More than a decade ago, The Wall Street Journal took a well-documented look at airplane water quality. Reporters collected water samples from airplane galleys (where attendants fill those water pitchers) and lavatory taps on 14 different flights. The water was sent for testing, and it was found to contain all sorts of unpleasant microscopic life, ranging from salmonella and staphylococcus to insect eggs.

"This water is not potable by any means," Donald Hendrickson, the director of Hoosier Microbiology Laboratories which tested the samples, told the Journal.

Who’s in charge?

Airplane water safety falls under the authority of several different agencies. The Food and Drug Administration (FDA) is in charge of the quality of airports' water facilities, which includes hoses, water lines and water tanks. The Federal Aviation Administration (FAA) is responsible for the on-board water tanks and requires them to be cleaned and flushed out regularly. When the water is on the plane, it’s controlled by the Environmental Protection Agency (EPA).

In 2004, the EPA did its own study of airplane drinking water. Water supplies on 15 percent of 327 planes tested positive for total coliform bacteria. Although those bacteria are harmless, they are indicators that other disease-causing organisms — such as E. coli or fecal coliform — could be in the water.

Although representatives from some of the airlines argued with the EPA’s methodology and findings, 45 of them made agreements with the agency on water-testing protocols until the Aircraft Drinking Water Rule was created in 2009. One of the main components of that rule is “routine disinfection and flushing” of the plane’s water system. The public must also be notified if there’s any kind of health risk.

What should you drink?

With this rule in effect, the hope would be that plane water is safe. But you still may want to think twice when the beverage cart goes by.

On its website, the EPA warns that passengers with suppressed immune systems or other health concerns may want to request canned or bottle beverages. The EPA also suggests they avoid drinking coffee or tea. According to the EPA website: “While boiling water for one minute will remove pathogens from drinking water, the water used to prepare coffee and tea aboard a plane is not generally brought to a sufficiently high temperature to guarantee that pathogens are killed.”

To be on the safe side, you may want to order a bottled or canned drink — or buy one after passing through security and bring it on board.

Some other water-smart safety tips when you’re flying the friendly skies:

Skip the ice. If you really want a very cold drink, ask the flight attendant for the source of the ice first. Find out if it was brought on board by a catering service or made on the plane with water from the plane’s tanks.

Brush with bottled water. Don’t use the bathroom tap water to brush your teeth. There’s a chance you could swallow some — which is bad news if there’s bacteria in it. Instead, take a bottle of water with you and your toothbrush when you head to the lavatory.