When you work out heavily for long period you will end up losing lots of water and you must be able to hydrate yourself in some way or the other. Having regular breaks and hydrating yourself in between a workout is a good way to hydrate the body. IF you are on the treadmill, then you can have a sip of water from time to time and make sure that you do not lose too much water. The amount of water you lose depends on your constitution and you need to replenish accordingly. Energy drinks are also a good way to hydrate the body.