My mother always gave me "jello water".... That was before Pedialyte was available! I googled it and found the following medical website which recommends jello water as one option for mild dehydration. See below:
For the child with milder symptoms ORS (Oral Rehydration Solution, like Pedialyte) is still best, but other clear liquids such as juice (any kind except Apple), flat soda, or sports drinks may suffice to prevent dehydration. The advantage is these may be easier to get your child to take. The disadvantages compared to ORS are that they may actually perpetuate the diarrhea (by virtue of their high sugar content) and they won't have the stomach-calming effect that ORS does.
Some "half way" (not as good as ORS but better than juice or soda pop) alternatives:
Chicken Soup alternating with other (non-ORS) clears.
Mixture of 2 parts ORS + 1 part Gatorade
Jell-O water (mix acc. to dir. then add 2 extra cups water)