@Lightlyseared is absolutely correct. The whole “stay hydrated” thing is baseless, a marketing ploy by the bottled water, soft drink, and sports drink industry. In general, all three types of beverages are manufactured by the same companies and distributed through the same channels.
Dehydration is seldom a concern for anyone who lives in a developed country and has access to clean, running water. Our marvelous bodies tell us when it’s time to drink fluids. During a very hot day, or during periods of extra physical activity, we know to increase the volume. The drink-more-drink-more mantra is just another non-problem causing worries and boosting beverage sales.
Please don’t get me started on 10 servings of fruits and vegetables per day. Or, is it 5–10 servings? I’ve also read 13 servings, minimum, or else die tomorrow.