[Coda]

Actually, two liters is sufficient; you're SUPPOSED to pee it out. If you're RETAINING that much fluid, something's wrong with your body. Your body will absorb what it needs and use the rest to flush out metabolic waste products like excess salts and excess water-soluble vitamins.

Edit: That is, 2 to 2.2 liters is sufficient for the average woman; some research indicates that men need as much as 3 liters. But as long as your urine is mostly clear (slightly colored is OK) you're probably hydrated enough.