Refilling your water bottle is an easy way to save money, be green and most importantly stay healthy, right? Wrong.

A study by Treadmill Reviews has found that water bottles harbor huge levels of potentially harmful bacteria.

In fact, researchers revealed that drinking from the average refillable bottle “can be many times worse than licking your dog’s toy.”

Gross.

Four different types of reusable bottle were tested after they were used by athletes for a week, and the results were shocking.

The study found that the average athlete’s water bottle had 313,499 CFU (colony-forming units of bacteria).

In comparison, the average dog toy has 2,937.

But some types of water bottle came out worse than others.

The slide-top water bottle may be handy to stop unwanted spillages while you pound it out on the treadmill or even while running for the morning bus, but it harbored the most germs.

The slide-top bottles tested had a whopping average of 933,340 CFU, while straw-top water bottles were a clear winner with a mere 25.4 CFU.

The classic screw-top bottles had 159,060 CFU, meaning that a swig from that is about as bad as lapping up water from your kitchen sink.

And the squeeze top had an average of 161,971 CFU.

However, although paling in comparison to the shocking levels found on the slide top, the squeeze top’s bacteria was a lot more harmful.

Nearly 99 percent of the bacteria found on the bottle was classed as harmful and there were traces of antibiotic-immune bacteria, such as the food poisoning-causing E. coli.

In total, over 60 percent of the germs found on water bottles in the study had the potential to make you sick.

So how do you avoid the bacteria hit without feeling like you’ve personally filled an entire landfill each time you reach for a new bottle?

Be smart about your choice and — if you can — opt for a straw-top bottle, which contained the fewest germs, the majority of which were non-harmful and naturally occurring.

The researchers also suggest choosing stainless steel over plastic bottles and not letting your half-drunk bottle sit in the bottom of your bag or back of your car for weeks.

They recommend running them through the dishwasher or using a weak bleach solution to give them a wash by hand after each use.

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