With a couple of PET-bottles, a (bike-)pump, tape, cardboard and some tools (and water) it is possible to construct your very own PET Bottle Water Rocket. According to Wikipedia, this is how it works:
1) Compressed air is added to the fuselage which creates a bubble which floats up through the water and then pressurizes the air volume in the top of the bottle.
2) The bottle is released from the pump.
3) The water is pushed out the nozzle by the compressed air.
4) The bottle moves away from the water because it follows Newton’s Third Law: For every action there is an equal and opposite reaction.
In 2007 the current altitude record for water rockets was set in the USA: 630m. But be care full, a water rocket is the real deal, that means that Newton works in other ways as well. The bottle can burst and what goes up, must come down.
PET Bottle Rocket (since … PET?)
Superused: Pet bottles
Recipe (inclusive a parachute): 2 liter PET (soda) bottles, water, strong and cardboard paper, glue, duct tape (or any other tape), clay, plastic bags, string, and a pump.
More how to: http://sections.asme.org/sandiego/Meetings/waterrocketconstruction.pdf
And than when succeeded one can calculate the altitude: