If you've been doing yoga asanas, you've probably noticed that they can cause you to perspire a lot, especially in hot climates. But don't worry, sweating is good for your health. It cools down the body and eliminates toxins. However, if you perspire a lot without drinking enough fluids, your body can dehydrate, and this can cause both minor and major health problems. In general, you should drink between 6 to 10 glasses of water each day. If it's hot and you plan to exercise vigorously, you can drink more. Some yoga asanas should not be done too soon after drinking. But an hour or two before you exercise, you can drink a couple of large glasses of water. Then, around 20 minutes before you begin your session, you can have another small drink. For example, if you drive to a class or to a park to do yoga, it's more sensible to drink well before you leave so you're not thirsty when you arrive. If you forget, though, a few sips of water right before you start won't hurt.
If you do yoga outside, the best times are in the morning and late afternoon when it's not too hot. Practicing in the hot midday sun may dehydrate your body and drain your energy.
Just remember that before you do asanas, you should empty your bladder. And if while practicing you feel the urge to go, go right away. Otherwise, you'll feel uncomfortable and won't be able to relax.