You avoid ice in your drink when you travel to certain parts of Mexico and other less-developed locales so you don’t suffer Montezuma’s revenge. (The usual culprit? Fecal bacteria in contaminated water.) But you can assume the ice on your road trip within the good ole’ US of A is perfectly safe, right?

Before you hit the hotel ice machine or even enjoy a drink on the rocks at your local watering hole, read this.

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The road to contamination

The fact that ice is cold helps keep in check some of the more common pathogens, such as E. coli and salmonella, which thrive in environments closer to our own body temperatures. But that hardly means your ice is germ free.

The culprit in most cases of bacteria- and virus-laden ice is likely poor handling or improperly maintained ice machines, says Robert W. Powitz, PhD, MPH, a forensic sanitarian based in Connecticut.

When your bartender jams that wine bottle into his ice bin or your flight attendant digs the plastic cup he’s holding (with hands that have touched just about everything on the plane) into his ice bucket, he can introduce germs into the cubes. One bug that could sneak in is norovirus, the top cause of food-borne disease outbreaks in the United States according to the Centers for Disease and Prevention (CDC).

"Norovirus originates in human fecal matter, and improperly washed hands are thought to be the main cause of contamination," said Karen Constable in Food Safety Magazine." Constable is certification manager of HACCP International, a food science and safety organization. "If you have ever seen a bar person drag a glass through an ice tub with his bare hands or watched an employee drop the ice scoop back into an ice machine bin with the handle coming into contact with the ice, you have seen a norovirus outbreak waiting to happen," she added.

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How likely are you to get sick?

Powitz maintains that getting an infection from ice is pretty rare, especially because the turnover rate is so high in restaurants, bars and on flights. There simply isn't time for large colonies of bacteria to grow on the ice.

The same doesn’t necessarily hold true for ice machines in hotels, however. Not only is the turnover rate lower, every guest in the hotel has access to the ice, and it's hard to say how many hands are plunging into the bin. What’s more, the ice machine itself may be cranking out less-than-sterile goods.

Even though ice is treated as a food by the Food and Drug Administration (FDA), which imposes strict rules on cleaning and dispensing, the rules aren’t always followed or enforced.

According to Powitz, biofilm can grow in ice machines that aren't properly cleaned. Biofilm consists of bacteria that have banded together in a colony; think of the slime that can form on the inside of a flower vase if you don't change the water regularly. Once it forms, it can be extremely tough to get rid of. "For instance, Listeria can be 1,000 times harder to eliminate if it is living in a protective biofilm and can be a continual source of pathogenic and spoilage organisms if not completely removed,” Powitz wrote in Food Safety Magazine.

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How to get clean ice at a hotel

"There's a good rule of thumb," says Powitz: "If you rent a hotel that's a known chain, they have a regularly scheduled cleaning of the ice machines and they do a credible job of it. The ones that I would be a little circumspect about are some of the low-rent independents. There you may find the film around the base of the catch basin of the ice machine and so on."

You can also take a few other steps to try to make sure your ice is clean.

Inspect the machine. If you see rust or grime, that's likely a good indication the machine it's not well maintained. Also, ice machines that have rounded edges inside might be a safer bet. "Nooks and crannies, joints and deeply squared internal corners are difficult to clean because cloths and brushes do not penetrate easily," said Constable. "A well-designed ice machine will have rounded internal corners on its ice chutes and ice bins, smooth internal surfaces and an easy-to-access, ice-making chamber."

Line the ice bucket. Line your ice bucket with a clean plastic bag before loading it up. The bucket might not be sanitized between guests and instead could be just rinsed casually by the housekeeper. So don’t assume it’s sterile.

Use a clean cup as your scoop. Skip the scoop provided. Just be sure not to get your own hands in the ice and cause a problem for the person who comes to the machine after you.

Buy bagged ice. If you're going to be staying at a hotel and you can’t live without your ice, you might do best to buy bagged ice before you check in. Powitz says the bagged ice industry tends to be a well regulated.

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If you’re healthy and follow these tips, you can chill

"The good news," Powitz says, "is you don't have that many people sick from ice." While people with a compromised immune system could catch an infection from unsafe handling, he says, healthy people don't have that much to worry about, especially if they follow the common sense practices above.

Powitz adds that the best time to avoid ice, or any food for that matter, is when the people handling it are touching lots of other things, which is why he himself avoids ice on an airplane.

Michael Franco is a science and technology writer who secretly wishes he was an astronaut. His work has appeared in CNET, and Discover Magazine.