Thirst: Physiological and Psychological Aspects

At one time or another, everyone has said "I am thirsty". Yet what causes this sensation of thirst? It is obvious that a certain quantity of fluid must be present for the body to function normally. How does a water deficit in the body then influence drinking habits? But supposing the physiological need is met, what about the psychological need or social need? Water is certainly the most necessary fluid; then why do we humans often prefer other beverages, even at great cost of effort or mone...