Water, Water Everywhere and Don't Forget to Drink!
Bring water to the poolside. Your body still perspires when you swim and you are constantly blowing off water vapor as you breathe. Drink before you get thirsty and drink more than you think you need.
Fish Fuel Out of the water, nutrition for swimming performance isn't markedly different from nutrition for running, hiking and cycling. You still need sufficient carbohydrates to fuel the workout and to reload in preparation for the next one.