A water wanker is one of those annoying people who uses very frequent breaks for water (and making everyone else wait) as an excuse to avoid/have time to recover because they can't hack a pace of a game/sport/workout.
Can we just play this game please?
No we can't because John is having yet another drink break - what a water wanker!
One who thinks his shit doesn't stink and is unyielding to bend the rules. An idealist who believes he's been bestowed divine right and believes he can "walk on water", literally. One who takes it upon himself to enforce any and all rules with extreme prejudice. A hardass.