bmumford.com, look under photography for a device called the time machine. i have worked with a few devices more expensive and this is the best hands down. it was created for brooks institute of photography, which is where i studied high speed photography. i have used his time machine for 7 years now, doing water drips, splashes, pours, drop tank, BB gun shots, and live ballistics with a bullet.
what ever system you use, you need an IR or laser beem trigger, laser is easier because you can see it, it will be out of the shot any ways and then connect the flashes to the control device. do a bulb exposure in the dark let the flashes expose the shot. i reccomend vivitar 283/285 series flashes for water action.
