A long time ago, I read a book called "Eat To Win". The author was once of the first to tell people they needed to drink water for sports performance.

His simple recipe for a sports drink was:

* Pint of water
* A few Tbsp of orange juice
* A dash of salt

Everyone's different. You need to tweak this so that your ingesting the sugars and minerals in the drink and it's not so concentrated that it sits in your stomach.