Hold your breath for as long as you can. And I mean, take a very deep breath and hold it in, don't wimp out. Works for me 100% of the time. Others swear by the spoonful of sugar which achieves basically the same thing as holding your breath -- giving your diaphragm time to relax.
And before anyone jumps all over me, yes there are more complex and serious reasons to get hiccups. But he probably drank that water too fast and the above should help.