When one is thirsty
Brocho before eating this: Shehakol Niyeh Bedvoro
Brocho after eating the proper shiur of this: Borei Nefashos
When one is not thirsty
No Brocho is required
(for example, using water to swallow a pill when not thirsty)
[drinking water to aid in digestion is considered "thirsty"]
Source: The Laws of B'rachos (pages 135, 384)