This just in: the more water you consume, the more happy you’ll be. It is suggested that men drink 3.7 liters a day; women should drink 2.7. Even if they don’t meet those suggestions, those who drink more water report being more happy, energetic and successful.
For more info and data on why, I’d recommend checking out this recent write-up via Ladders. The reasons for staying hydrated, as well as other health benefits, might surprise you.