Every time you take a sip from your water bottle, you are depositing bacteria inside and over the course of a day these can multiply by the millions. Here's what scientists say you can do about it.

Practise and challenge your friends! Download the Water bottle Rockets PDF(378 Kb). Adobe Acrobat is required. SAFETY: This rocket uses air pressure to fling a bottle at high speed 20–50 metres.

Whether you need a bottle that keeps your water ice-cold for hours, one with a built-in straw for effortless sipping, or a rugged adventure-ready option, our guide breaks down the best of the best.

What horrors grow within? Credit: Eyeem / Getty Images It takes a lot of grime for a reusable water bottle to look dirty. After all, it's usually just water in there. Bad news, though: If you're ...