While most airlines have ceased offering free snacks and food for some time now, at least that drink cart still comes down the aisle as passengers wait eagerly with parched mouths. Juices, sodas, coffee, tea, and water are offered at no additional cost, and flyers pick their favorite beverage with no second thoughts.

But what if you learned that there are some drinks even the flight attendants wouldn't take a drop of? They may be serving it up, but you won't see too many of them chugging it down. Coffee and tea are the beverages being frowned upon, due to the water with which they are made. Plain cold water is usually from a bottle, so that's why H20 still gets the A-OK.

Why the nix on coffee and tea? It's because the water is kept in tanks on the plane, and according to various studies, these tanks aren't too clean. According to an NBC Investigates report, "That tank is filled at airports in all different cities. And sometimes the hoses used to fill the tanks are filthy."

As per Business Insider, "An EPA study found that 1 in every 8 planes fails the agency's standards for water safety." A regulation by the Environmental Protection Agency, "gives broad discretion to airlines on how often they must test the water and flush the tanks. AFA does not believe this regulation goes far enough or is sufficiently enforced." And you thought the tray tables were dirty.

As per NBC Investigates, "12 percent of commercial airplanes in the U.S. had at least one positive test for coliform. That's just about one out of every 10 planes. Coliform itself is not likely to make a person sick, but it can be a red flag that other bacteria, like E. coli, have made their way into the water."

Heating the water will not kill off this bacteria - only disinfection will do the job - but this process is not in place. As per Safe Bee, "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, 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."

So if you're seeking a caffeine pick-me-up, go for aCoca-Cola rather than airplane coffee or tea. You may not get sick if you do take the chance and go for a hot beverage, but knowing your drink may not be sanitary is sickening in itself.

Follow the lead of the flight attendants. They're looking out for our safety in more ways than one.