1/2 your weight in oz of water should be fine, especially if when excersising; for me that's 100 oz of h2o a day. I wind up using the facilities about every 1 1/2 hours.
"...
At least eight eight-ounce glasses of water a day for all adults, most of whom lose about two to three quarts (64 to 96 oz) of water every day. Athletes, people who live or work in hot environments, and people who perspire heavily lose more water and need to drink even more to keep up with the loss. "
Link to full article http://www.webmd.com/content/article/41/1671_50514.htm
"...
At least eight eight-ounce glasses of water a day for all adults, most of whom lose about two to three quarts (64 to 96 oz) of water every day. Athletes, people who live or work in hot environments, and people who perspire heavily lose more water and need to drink even more to keep up with the loss. "
Link to full article http://www.webmd.com/content/article/41/1671_50514.htm