Most teas, caffeinated especially, but also a lot of herbs, have a diuretic effect on the body whether they are consumed hot or cold. This means that for every ounce of tea consumed, your body expels an ounce and a half of water. So just be sure to drink extra water to make up for the diuretic effect...this goes for coffee, juice and sugary beverages as well.
According to Dr. Batmanghelidj, your body starts to rely on the concentrating power of your kidneys to retain water if you're beginning to become dehydrated. If your urine is light, then you should be well hydrated :)!
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