the first time i went on a 9 mile hike with a walking group they down played the water i would need, i guess because they were acustomed to walking and had conditioned their bodies for it. so i showed up with a measly bottle of water. i ended up drinking it and half of theirs it was embarassing. but i was not conditioned for it.
so i totally agree with Jeremy, depends on your body, better to have too much than not enogh. do you have a camelbak? might be a good idea to buy one with the largest reservoir possible. i would also add that it helps to make sure some of the liquid is a sports drink as it will help replenish your potassium and other minerals you lose while sweating. have fun on your walk!
