Whats the best thing to take for water retention?

Treat the cause: Water retention is a symptom of some underlying problem. The trick is to figure out what that is and treat it. The answer is often diuretics ("water pills") but the cause will determine what kinds of diuretics or even a different treatment entirely. Definitely need to see your doc for this.

Diuretics: Limit your salt intake to less than 2gm/day and if you have a lot of swelling in feet then water pills or diuretics such as hctz (hydrochlorothiazide) or Lasix are very effective.