The simple technique I used was to lay with my head just above the water, fully engulfed up to where my mouth and nose were just above water, so I could see the surface of the water closely and also to block our ambient sounds since my ears were also under water. Then breathing slowly and fully, I'd concentrate on the sound and sensation of inhaling and exhaling, and I'd try to minimize any break in the surface of the water. Doing this for just 15 minutes, my heart rate would slow down, yet I'd also fully awaken.
Beginning the day with a relaxed and aware mind state instead of one agitated in caffeinated state made a big difference in productivity and also health (and there was plenty of time later in the day to get buzzed on coffee or soda if I needed the boost). It also made me a nicer commuter and morning person in the office. Even now, though I don't work in that crazy office environment, I still begin each morning with a slow and relaxed bath; I don't always need to meditate, but when the need arises, all I have to is set aside 15 minutes to slow down and rejuvenate. Give it a try.
[photo credit: arboresce]