A few friends have really expressed interest in this shot so I thought I would do my best to explain how I took it.
First of all, I highly recommend getting the book "Light, Science and Magic". It is by far the single best resource I have come across on mastering lighting techniques, other than the Strobist blog. Its a valuable tool to have around.
With this shot, I wanted the glass and water singled out on a white background. Since the glass and the water are almost completely transparent, I realized that direct flash would not do the trick. Reflected light would be the best answer. I have to admit also, that I have been researching how to do this shot for some time, which is how I came up with my setup. So... that being said..
The glass was placed on a table with black formica underneath. Then I placed a piece of black cardboard with a sheet of 8.5" x 11" white, photo glossy paper in the center of the black cardboard, directly behind the glass. The white photo paper was my "reflector" of the light and the black cardboard is what gave the water and the glass the black outline.
Then I placed my Nikon SB-800 under the table, closer to the back side, and pointed the head towards the piece of white photo paper. This was my only light source used. By placing the flash underneath the table, I prevented light from spilling on to my glass and water, in other words, I gobo'd the flash.
Click on my "high tech" illustration for a bigger view. Da Vinci has nothing on me! =)
For the exposure, I set my Nikon D300 to its fastest native flash sync speed (I say native because you can actually trick the camera into using much faster sync speeds than the factory default) and set my aperture to f/11, my ISO to 100. The flash was on 1/16 power at this time. I took a test shot, and it was quite a bit too bright for my liking, so I stopped down my aperture to f/16 and decreased my flash power to 1/32 and took another test shot. I liked this result.
Originally I wasn't planning on pouring water into the glass. I just wanted a nice photo of the glass itself, but since my roommate was home, I decided to use his extra set of hands and conned him into helping me. He held the water in a small measuring cup directly over the glass and on my signal, began pouring the water. As luck would have it, I got it on the first take.
I hope this explains the technique I used, and if you have any questions, please don't hesitate to leave me a comment.