Once upon a time, the world was flat. Now it's round. Who knows? Maybe some day we'll find out it's square. It's hard to come across a cold hard fact anymore. Drink 8 glasses of water a day. Drink 16 glasses of water a day. Don't drink any water; get all your water from fruits and vegetables. The contradictory advice goes on forever. There's almost nothing you can nail down with absolute certainty. Even your own content.