Why Doesn’t Saliva Quench Your Thirst?
In an effort to answer a question that may or may not ever have entered your mind (until just now), we bring you this explanation:
Since saliva is 98% water it stands to reason that it should serve as a thirst-quencher, at least to some extent. But, as anyone who has ever died of thirst in the desert or dropped his water bottle into an open manhole while jogging can tell you (well, maybe not that first guy) -- that is not the case.
And the reason for that starts with the fact that saliva is more concentrated than water is. It’s chock full of proteins and enzymes. That’s a good thing for its purpose -- mainly a lubricant, making food easier to swallow and digest -- but not for a satisfying drink.
Water, on the other hand, is far less concentrated with salts and other solutes than the fluids in the human body, and that's why it's so refreshing to drink when you're thirsty. What’s more, when you're thirsty your saliva gets even more concentrated because your body has less water to spare.
Finally, how can you tell if you're dehydrated? The best way is to look closely at another bodily fluid, your urine. When your body is lacking fluids, it goes into survival mode and holds on to all of its water, meaning your urine will be very concentrated and less watery. Basically, if your urine is very dark, resembling the color of iced tea, you're probably dehydrated.