How many bacteria live on your water bottle?

Research commissioned by reveals thousands of bacteria on an unwashed bottle

Watch the peloton screaming towards a sprint finish and you can’t help but notice the stream of bottles being launched off sideways. Pro riders go through huge numbers of bottles – over 40,000 on the Tour de France – using each once then throwing it away.

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Pros use a lot of bottles - this is for one stage of the Tour of Oman. Credit Watson

Pros use a lot of bottles – this is for one stage of the Tour of Oman. Credit: Watson

It looks profligate, but it turns out that they may have the right idea according to research commissioned by, who counted the bacteria on the surface of popular designs of refillable water bottles. And there are lots.

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Swabs were taken from the lids of reusable bottles which had been used without cleaning for a week. The swabs were tested by a lab to determine the numbers and types of bacteria present, measured as colony-forming units (CFU) per square centimetre.

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The average number of CFUs on the 12 water bottles sampled (three for each design) was 313,499. This compares with 2,937 found on the average dog’s toy and 3,191 in a kitchen sink.

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The worst were slide topped bottles with over 900,000 CFUs found. This was followed by the cyclist’s favourite, the squeeze top, with around 160,000 CFUs. Screw topped bottles came out about the same, but bottles with straws came out cleanest at only 25 CFUs per square cm – around the same number as on a toilet seat.

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Keep it clean!

Keep it clean!

The tests also found that around 99% of bacteria on squeeze top bottles were Gram negative – the same category as E coli – and potentially harmful.

Treadmillreviews recommends stainless steel over plastic bottles and thoroughly cleaning out the bottle after each use. It also suggests weak bleach to make sure the bacteria are definitely dead.