During a run, long walk or hours-long meeting at the office, your water bottle is a life saver, at the ready when you need a swig to keep you going. While keeping you hydrated, a reusable bottle also helps you do your part to save the planet — no contributing to the sea of plastic bottles that make up the Great Pacific Ocean Patch for you.

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All's well until that day you take a swig and notice a funny taste or, worse, a funky smell.

Yes, reusable water bottles are planet-friendly, but they do require some care and attention. With enough neglect, they can grow all kinds of things. And if you share your bottle (not advised by germ experts), you're asking for even more trouble, especially if you are big on sharing yet lax on cleaning.

Here, how to know if your bottle is a germ trap, what types of bugs your bottle can pass on and how best to clean it so you don’t get sick.

Which bottles are germ traps

The reusable water bottles with the pull-up, push-down tops are bigger germ traps than ones with screw-off caps, says Chuck Gerba, PhD, professor of microbiology at the University of Arizona, Tucson, and a long-term germ researcher (also known as "Dr. Germ").

"You push down with your thumb [to close it]," he says. And when you go to pull it up for a drink, ''you contaminated where you are going to put your mouth," he says. Water bottle models with the screw-on, screw-off lids still can carry bugs, but there's less risk of contamination, he says.

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What can bottles pass on?

If you don't share your water bottle, you don’t need to be too concerned about catching a nasty bug, Gerba says. "If you share it, the big concern is you can get a respiratory infection — a cold or the flu," he says. You might also get strep throat, he says, or even herpes if the thirsty borrower has a cold sore.

With the sports-type bottle with the pop-up, push-down top, you have to worry about the possibility of catching respiratory infections plus diarrhea, he says, since whoever's thumb is opening it could have picked up a ton of germs from many places, including the bathroom.

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How to clean your bottle for best results

Washing the bottle regularly (some experts advise daily) can help reduce germs. "If you have a wide enough mouth on the bottle, put it in the dishwasher," Gerba says. Be sure it dries completely during the drying cycle. If it's still moist, let it air dry completely.

If the bottle has a narrow mouth, hand washing is better, he says. Plain dishwashing soap and hot water will do the job, Gerba says. (In a study on cleaning dirty dishes, Gerba found equal results with antibacterial soap and regular soap. He suspects the same would be true for water bottles.)

After hand washing the bottle, rinse it thoroughly and put it on a drying rack. "Let it dry on the inside," Gerba says. Drying the inside is thoroughly eliminates the moist environment that allows bugs to thrive.

If there is buildup of gunk inside the bottle or you've been lax about cleaning it, you may want to use a bottle brush to scour the inside of the bottle before washing it, advises the Nalgene company.

For funky tastes or odor, give your bottle an over-night treatment, suggest experts at REI. Put a teaspoon of bleach and a teaspoon of baking soda in the bottle. Let it sit overnight. The next day, rinse the bottle thoroughly or, if the mouth is wide enough, pop it in the dishwasher. Dry it completely.

Some suggest cleaning the bottles with vinegar, but Gerba doesn't buy that. "It will make it smell like a pickle, and it doesn't kill the organisms you want. Vinegar is somewhat antimicrobial, but it doesn't kill noroviruses (the kind that often spread on cruise ships) or respiratory viruses."

Specialized sport bottle washes are available, too, but not necessary, in Gerba's view.

What about disinfecting? Not necessary either, Gerba say. However, he adds, "if there is a concern I would just use a little bleach. A tablespoon of bleach in a quart of water." Rinse thoroughly in clean water, of course.

Aim for almost bug-free

Even meticulous cleaning is not foolproof, Gerba says. You can clean the water bottle thoroughly, he says, but "you can never make it bacteria-free."

And we had to ask: what sort of bottle does Gerba use? "I don't use the reusables," he says. But his wife, Peggy, a Boy Scout leader and intrepid outdoorswoman, does. "She uses the metal ones that screw shut," he says. "I make sure she washes them." And his other rule, of course, is ''no sharing." Not even with a thirsty Boy Scout. 

Kathleen Doheny is a Los Angeles journalist specializing in health, behavior and fitness topics.