water rockets work on compressed gas (normally air) which sits in a "pressure vessel" (normally a PET bottle) with an amount of water between the gas and the nozzle. the pressure of the gas forces the water out of the nozzle, and the reaction force is the thrust.
The controlling parameters in the design and performance of the water rocket are:
 the amount of water, the nozzle dimensions, gas pressure, and aerodynamic properties of the rocket body.

Multi staging is acheivable, but the real "R&D" of water rockets seems to be directed towards the development of recovery systems.

Hope this helps,
Des

>>> Mark Willis <mwillis@NWLINK.COM> 6/29/99 8:15:03 pm >>>
"Inquiring Minds have to know":  How does one LAUNCH a water rocket?
(Reply off-list or on, I just want to know <G>)  Hopefully it's
electrical & attached to a PIC.

I've seen Magnetic and optoelectronic "Launch" detectors in model
rockets, btw.  A piece of electrical tape can serve to interrupt the
opto, so long as it's not IR - then you want to add a piece of aluminum
foil inside the tape <G>

Admin note:  We're getting duplicate messages & some people are getting
"You shouldn't send duplicates to the PICList" error messages, known
problem, should be solved soon.  Someone's ISP is messed up, I'm being
patient.

  Mark