Here's a link to a site that investigates urban myths, discussing a water-related topic.
http://www.snopes.com/medical/myths/8glasses.asp
I'm not saying you shouldn't drink water, but the evidence that we need 8 glasses of water a day to remain hydrated seems to be lacking.
Although I don't have the link for it offhand, one of the more interesting parts to this debate is what counts as water. The original doctor who raised the 8 glasses a day issue stated that the water could come from other sources -- including caffeinated drinks and foods (like fruits and veggies). However, his caveat seems to have turned into its opposite!
Anyway, again, I'm not saying that drinking water is bad, and it may have benefits beyond hydration too! But water can come from many sources and we may not need as much "straight water" as we are sometimes told