Pedialyte if you can choke it down.... I cannot.
Yeah this. It turns out evolution did a pretty good job with the kidney (don't mean to brag or anything ). When you are dry you will feel thirst. Water does a great job at fixing that. Barring underlying heart/kidney disease, your body will hold onto all of the salt it needs until you are volume re-expanded.
Pedialyte and similar are really best used for intractable diarrhea. The sugar in these drinks helps your gut take up salt that it is otherwise wasting because of the cytotoxic effect of GI bugs on your colonic mucosa. Gatorade works too but not quite as well per oz so you have to drink a lot more. Expect interesting colors in the toilet bowl.