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If you’re exercising for more than an hour, that’s when the question of what to drink shifts from the obvious—water—to the more complex—sports drinks. The latest entrant in this $7 billion-a-year business is , a powder you add to water that offers six times the electrolytes of the normal sports drink and half the calories and sugar.

Working off rehydration guidelines established by the and information from the (showing that the average person loses between 550-725mg of sodium per liter of sweat), SOS injects 660 mg of sodium into each of its packets, in addition to the electrolytes chloride, potassium, citrate, and magnesium.

That may seem like sodium overkill, but it might be just right depending on the athlete and what she’s doing. “People’s fluid needs are dependent upon their sweat losses during a particular exercise in a particular environment,” says Dr. Susan Yeargin, assistant professor of athletic training at the University of South Carolina. “Everything always depends on the situation—there is nothing cookie cutter about hydration.”

Following the rule that water follows sodium, and that a small amount of sugar is needed to help the body, especially your gut, absorb the sodium, SOS also added the sugar substitute stevia to the mix. That not only sweetens the drink, and offsets that chunk of sodium, it also speeds up the water-absorption process, SOS’ creators claim. Result: you rehydrate more quickly.

So is SOS any better than the competition? Top sellers such as Gatorade, Powerade, and Propel are all, Yeargin says, “effective.” What likely makes them so popular is that they also taste better than most other sports drinks. “Research shows that if an athlete likes what they’re drinking,” says Kimberly Stein, a senior principal scientist at the , “they’ll drink more of that.”

The key, then, may just be in finding the one drink you like—because it tastes good, because it’s pretty, because it has just the right scientifically proven balance of electrolytes and carbs and sugars. Whatever the reason, you’ll actually drink it. And stay properly hydrated. But whatever you do, ��Dz�’t stay thirsty.