Oh gee, I just drink water whenever I'm thirsty. That amounts to about oh, maybe 24 oz or less per day? And I've been at this for my whole life.
All around the world people drink water when they're thirsty, not by some seemingly arbitrary measure set by their government.
Louis Black has a hilarious commentary on the subject. He notes that interestingly enough, we suddenly now had to drink 64 oz of water a day around the same time that companies started bottling and selling plain water... how convenient, neh?
1) eat real food - more vegetables, moderate meat, moderate fruits, less grains, less sugar, less vegetable oils.
2) exercise - moderate intensity cardio, sprinting, heavy lifting, dedicated stretching and mobility.
3) live - relax, de-stress, meditate.
Disclaimer: I'm not professionally qualified to make any formal recommendations. I've just done my homework and I'm my own guinea pig. All of my data, unless otherwise cited, comes from a sample size of n=1 (me).