Splash Photography

You need a flash with a shorter duration, try lowering the power and see if that helps.

As Bob says.
Your shutter speed is almost irrelevant, you should either use a high end studio flash such as Profoto or, if you can manage with low power and a limited ability to modify the light, hotshoe flashes will be fine.

The AB 1600 actually has the shortest flash duration at full power, but its not all that fast
AlienBees Specs Chart
Most studio lights are at there fastest at full power and flashes at the lowest settings, Vivitar 285's are cheap and have a very short flash duration
also watch for bounced flash (refectors, foam core...) sounds crazy but 2 fast flashes (direct then bounced) make the splash look like you shot it with one long flash duration (a little blur)

Thanks you guys. I've been pulling my hair out trying to figure this out.
What would be a sufficient flash duration? - I think my local camera shop has dynalites available for rent. Will they do?

The shutter speed is most certainly NOT irrelevant if this is being shot in bright conditions. Even at 1/125 of a second, some motion blur in the water can occur even at higher f stop settings. The specular highlights on water are mirror bright and will easily show a blur in this situation.

Believe it or not, small portable shoe flashes like the Vivitar 283 or 285 used in auto mode and put close to the subject can almost stop a bullet in flight. The thyristor circuitry is designed to cut the flash off after an extremely short duration in these close up conditions where-as the normal circuitry in most studio strobes is designed for a longer flash duration. If I remember correctly, the 283 can fire in as little as 1/50,000 of a second. Perhaps someone out there still has their instruction book and can verify or correct that figure.

Try a very different light set up where you are shooting in almost total darkness, just enough light to aim where to toss the water....no modeling lights, just a dim lamp somewhere way off the set. You will have preset the focus and all controls and can even use a slower shutter speed since there will no residual light that records...just the flash exposure. Then just fire the shutter when the water hits the subject.

Be sure that you use the flashes in battery mode. Hooking them up to AC adapters in a watery environment is inviting disaster!!

"The shutter speed is most certainly NOT irrelevant if this is being shot in bright conditions."

Wow, never even thought it could be outside.... for some reason my mind went to only the water/motion stopping part (drips, pours, beer mugs....) usually done inside where shutter speed would not be an issue.

Indoor or out to make sure your 1/250th a second will not be an issue, just find you working aperture and fire one off WITHOUT the strobes, if you get a perfectly back frame you are good to go, if you get an image of any kind its time to turn up the power of the lights to get smaller working aperture.

Raymond,

This doesn't even have to be outside for motion to record in the specular highlights if the modeling lights are bright enough. With most studio systems operating at relatively long burn rates, if the ISO is too high and thee is enough light in the room, motion may show up.....not in the subject, but in the specular highlights on the moving water.

That's why I suggested the Vivitars or another small flash with a thyristor type of circuitry which allows for extremely fast cut off rates. With only enough light in the studio to make out where to aim the water and for the model to know where to look, Chris should be able to avoid any semblance of motion in the splash.