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.

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 ...