Hydration

Swimming is a strenuous sport that can induce dehydration, cause fatigue, muscle cramping, and an overall poor level of physical performance. In its more advanced stages it can cause hyperthermia, heat exhaustion and heat stroke.
It is therefore vital that swimmers have plenty of fluids before, during and after training and competitions.
Read the link below regarding sports drinks!
Remember your drink bottle!
Nutrition

Below are some links which provide some good advice regarding nutrition and hydration.
Making the perfect recovery sandwich
Healthy Meals and Snacks for Athletes
Just how bad is sugar for our health?
The benefits of whole grains for swimming and weight loss
The dangers of carbo-loading for swimming