Exercising in hot weather can quickly cause dehydration if you don't drink enough fluids. The American College of Sports Medicine recommends the following to help active people avoid or minimize the effects of dehydration:

• Drink about 500 ml (17 oz) of fluid 2 hours before exercise to promote hydration while allowing sufficient time to excrete any excess water.
• Drink fluids before and during exercise at intervals frequent enough to replace the water lost by sweating (which can be 2-6% of your body's total weight during prolonged exercise, especially in hot weather).
• Fluids should be cooler than the surrounding air, flavored if desired, and in containers that are easy to use during exercise.
• If your exercise will last less than 1 hour, there is little evidence that drinks containing carbohydrates or electrolytes will provide any physiological or performance advantage over plain water.
• If your exercise is prolonged (lasting more than an hour) and especially intense, then performance can be maintained and fatigue delayed by drinking fluids containing carbohydrates (glucose, sucrose, maltodextrin).
• If your exercise will last longer than an hour, include small amounts of sodium to replace that lost in sweat.

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