http://www.outsideonline.com/fitness...sponsibly.html
For some reason, that page is missing the formula in the sidebar, but I saved it from that issue:
Jeukendrup's hydration recipe:
0.5 cup maltodextrin
6.5 tsp fructose
0.25-0.5 tsp table salt
Combine in one liter of water, shake, and serve!
I usually add instant green tea for flavoring.
You can get maltodextrin and fructose from places like
http://www.bulkfoods.com/