It’s common knowledge that drinking salt water when you’re dehydrated is dangerous. Yet in the days before sports drinks, the first thing we got for dehydration during football practice was salt tablets with water. What’s the difference?
—E.S., Knoxville, Tenn.
The main difference is the amount of salt. When you’re dehydrated, you need water, all right, but you need electrolytes (the scientific term for various salts) to survive too. Seawater has way too much of these salts, which can cause you to become more dehydrated than if you hadn’t drunk anything at all. But if you’re both dehydrated and low on salts—which is common in extreme physical activity, especially when you’re sweating heavily—and you drink only fresh water (which has very little salt), you will develop an electrolyte imbalance. Electrolytes are necessary for basic cell functions, and symptoms range from mild to severe. You can die from a lack of these salts; hence the old-fashioned salt tablets to prevent this from happening. They’re not used much today because they typically provided only two of the necessary electrolytes (sodium and chloride), and they could easily provide too much of them if not enough water was drunk at the same time. For extreme exercisers, modern sports drinks do the job much more safely.