What I'm thinking is that it might be fairly simple to take a tray, fill it with water, and then place a semi-permeable membrane across the midpoint of the tray dividing one half from the other. You may be able to place electrodes of some sort in each half of the tray to measure the current or voltage flowing across the membrane, by using a multimeter (it is a small device that measures current, voltage, resistance, etc.) You could then see how this measurement changes after adding different types of sports drinks or other drinks. Any changes may suggest that the electrolytes or other chemicals in the drink are increasing (or decreasing) electrical activity across the membrane relative to unenhanced water.

Sports drinks have both electrolytes and carbohydrates in them. Electrolytes function in maintaining proper water balance in your body. Carbohydrates give you energy (measured in Calories and found on the nutritional label.)

I looked quickly online for other science fair projects that measured electrolytes in sports drinks and came up with a couple.

projects_1

projects_2

This website tells you about measuring conductivity in fruits/fruit drinks.

counductivity