I think Kool-Aid was probably the 1st as evidenced by this excerpt from Wikipedia; I know I've been drinking it over 50 years:
Sounds like Gatorade for adults. I think someone said it's available there. Sounds like Pedialyte for infants. They both contain sugars and salts (potassiums/electrolytes) and starches (carbs) That does give it a somewhat salty taste also though. I like it but others might not.I was just about to post a query re best/cheapest rehydration powders which met the following NHS advice
If you are dehydrated, you will have lost sugar and salts as well as water. You should, therefore, drink a rehydration solution that contains all the essential ingredients that you need to re-establish the right balance of body fluids. The solution should contain a mixture of potassium and sodium salts, as well as glucose or starch...