Daily intake of 8+ glasses (8 oz. / 250 ml) of water for normal activity or half your body weight in oz. Drink more during the summer or if you spend time outdoors.
At least 2 hours prior to class drink 16 oz. / 500 ml of water. Stay away from fluids containing alcohol, caffeine or lots of sugar.
Take a water bottle into class with you and take small drinks between postures (after Eagle Pose). Be conservative with your water breaks; sometimes drinking water can become a habitual distraction.
Re-hydrate after class with an additional 32 oz. / 1liter of water. You may want to consider taking an electrolyte supplement to replace trace minerals, ideal for sports performance, people working in high temperatures and anyone experiencing high levels of fluid loss.
Refrain from wiping the sweat off your skin. If the sweat is removed from the skin, evaporation will not occur, and heat will be retained.
BEWARE of caffeinated and/or alcoholic beverages since they increase fluid loss and cause dehydration. In addition to your normal water intake, drink an equal amount of water to every glass of alcohol or caffeinated beverage.
This is a general guideline, you must find out for yourself what works best for you, but be aware that most of us do NOT drink enough water.