With just a few weeks to go before kids go back to school, parents are starting to think about buying the year's supplies.
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For many children, that will include a reusable drink bottle in an effort to stay healthy and hydrated.
But beware: water bottles are a perfect breeding ground for bacteria.
In a laboratory test covered by US television station KDVR, scientists swabbed a selection of drink bottles to test bacteria levels.
The test used 'colony forming units' (CFU) to measure the number of bacteria or fungal cells in a sample.
A maximum of five CFU is considered acceptable.
But one of three drink bottles had more than 100,000 CFU per swab.
For comparison, a swab from a dog bowl contained 700 CFU.
The owner of that drink bottle said he washed it once a month in the dishwasher.
The microbiologist leading the test said the result was "pretty nasty".
"We couldn't even count it, it was so full of bacteria."
Another bottle, reportedly rinsed daily, returned 6000 CFU per swab.
While existing bacteria in the human body will kill the majority of drink bottle bacteria, it's a good idea to wash bottles daily with hot, soapy water.