Drink about 1/2 to 1 cup (118 to 237 milliliters) of water every 15 to 20 minutes during your workout. Change amounts related to your body size and the weather. Drink roughly 2 to 3 cups (473 to 710 milliliters) of water after your workout for every pound (0.5 kilogram) of weight lost during it. More @Wikipedia
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