It is estimated that your body loses between one and two pounds of water per hour that The first thing I would recommend is eating a meal one to two hours before a workout. It doesn't need to be super filling, you just need to be able to fuel yourself for the workout. I myself don't like eating anything super heavy so I just try to aim for a piece of fruit and a bowl of oatmeal. Those are two things that are super easy to digest.  The next thing I would bring is a water bottle. I coach kids and one of the girls I coach probably drinks two 20 oz water bottles during an hour and a half of practice. I think to myself between the speed work and distance we do they probably need it. you swim. When you read that you gotta think that is a lot of water. It is a lot of water, but after swimming for years I could think that that fact is definitely feasible. We would never realize that we are losing all of that water due to the fact that we're in the water. The water keeps you cool, so they say it’s hard to tell if you’re sweating. Regardless, it is very important to keep a water bottle near your pool lane. A workout experience can change depending on whether you are hydrated or not.