What is dehydration?

Dehydration occurs when your body loses more fluid than you take in. When the normal water content of your body is reduced, it upsets the balance of minerals (salts and sugar) in your body, which affects the way it functions.

Source: Dehydration @ NHS Choices

Image: Water Impact 0 by (Henningklevjer) - (Henningklevjer). Licensed under CC BY-SA 2.5 via Wikimedia Commons.