Regulating Body Fluids In The Body

First, fluids are absorbed through the gut and into the bloodstream faster when their permeability closely matches that of body fluids such as blood.
Sports drinks contain dissolved minerals (sodium, etc.) and carbohydrates, whereas water doesn’t, so water doesn’t reach the bloodstream as quickly.
Sodium and other nutrients also play important roles in regulating fluid balance in the body. In other words, they help determine how much fluid enters into muscle fibers and other cells, how remains in the blood, and so forth. Again, because sports drinks contain these nutrients, they do a better job of allowing the body to maintain optimal fluid balance,