Shooting for at least an equal number of ounces of water to half your body weight is a number I have read in several articles. When you add exercise to your daily activities, you also need to add more water.
Try drinking: 12-20 oz. of water before exercise (usually after I wake up)
8 oz. (at least) every 20 minutes during exercise.
12 oz. post workout
I carry my water (camelbak) around the gym and consume 30-40 oz. while I workout. There's always the drinking fountain. Some people don't like water. Post workout, I like to drink a G2 or something like it. I tried the Nuun tablets, they worked as well. drink what works for you. Stay hydrated.