Studies on coconut water have been done for decades. However, there haven't been studies on coconut water and water for hydration and performance for athletes. Coconut water has been put up against sports drinks and water in the latest studies. The results may surprise you more than you think!
In the study athletes rehydrated after exercise with coconut water, sports beverages, and water. The rehydration actually wasn’t significant between any of them. The coconut water didn't hydrate the athletes more than the water or the sports drink. Additionally, scientists tested to see if performance in athletes would increase after drinking coconut water, sports drinks, or water. There was no significant difference between any of them! Plain water did give athletes a slightly higher performance (the cyclists were five seconds faster than those that drank coconut water or sports drinks), however not significant enough to make a difference.
The only side effect that really came to the forefront was that some of the athletes testing the coconut water had bloated and upset stomachs, something neither of the water or sports drinkers had. I would recommend sticking with water and not drinking the sports drink (not very healthy).
If you like coconut water the only piece of advice I would give you is to be cautious if you have kidneys that are not functioning very well. Coconut water has a large amount of potassium, and it can hurt people with lower kidney function. If you are low on potassium in your diet then coconut water may be a good source for you, but be aware of the foods you are eating so you don't overdo it.