Go ahead, pinch and see. If you pinch your skin on the back of your hand and it doesn't snap back right away - if it just stays up like a little crepe-y tent of skin - you're well on your way to severe dehydration. We learned the signs of dehydration from the guys over at SciShow and you should too. Stages of dehydration go from mild to severe and it gets gross. Your eyes start to sink into the back your head!
So, unless you're interested in mummifying yourself, when you're out and about don't forget to drink up.