Coconut water is so hot right now. No less than muscle queen Madonna digs it (so much so she bought in to one coco water company, Vita Coco). But are its claims to be a natural sports drink replacement legit? Not for most of them! Still, they are a good source of potassium for people who hate bananas. (Who ARE you people?)

ConsumerLabs compared the three major coconut water brands (O.N.E., Zico and Vita Coco) in a lab [Reg. Req'd] and found that as far as electrolytes go only one brand, Zico, lived up to the stats listed on their packaging. The other two tested had only 18 and 59 percent of the brands "promised" levels of sodium. Of course, you only really need to soak in lots of electrolytes for rehydration purposes if you have been sweating for more than an hour while doing heavy exertion—like training for a marathon.

"This is a major focus of the marketing for coconut water," Dr. Tod Cooperman, president of ConsumerLab, said. "When you start making claims comparing it to sports drinks, you expect them to at least deliver on what they are promising. People should be aware that the labels are not accurate on some of the products, and they shouldn't count on coconut water for serious rehydration."

On the plus side for coconut water? All three major brands do at least offer their promised "good source of potassium," which is an important part to maintaining muscle nerve functions. Also, some people actually truly like the taste.