SlipperySnake

Always wanted to build a rocket, but were afraid to use all the stuff that burns or explodes? Apparently you don't need to! All that's required is some water. Plastic bottle, which is also easy to find, is filled with water. Then pressurised air pushes the water out through the rocket nozzle and provides thrust for the rocket.
Detailed plans and video of the flying rockets including from the camera mounted on one of the rockets can be found on this web site.
You will of course need an air pressure device (air pump), which is a bit harder to find, to build up the air pressure up to 120psi that is required to push the water out of the bottle. You can get those from either a DIY store such as B&Q or online for around £10-20.