On average, you should take a rehydration break about every 20 minutes. Most people would stay adequately hydrated by drinking 5 to 10 ounces of fluid every 20 minutes. But your exact need depends on things like how hard you’re working, whether you are indoors or outdoors, and your age, gender, and weight.
It’s also helpful to drink two cups of fluids (about 16 ounces) about two hours before a workout.
General guidelines are to drink 17 to 20 ounces of water 2 to 3 hours before exercising, another 8 ounces during your warm-up (or 20 to 30 minutes before exercising), 7 to 10 ounces every 10 to 20 minutes during exercise, and 8 ounces of water within 30 minutes after exercising.
Drink fluids throughout the day before you exercise. … One to two hours before your workout, drink 15 to 20 ounces of water. 15 minutes before you begin, drink between 8 and 10 ounces of water. During your workout, drink another 8 ounces every 15 minutes.