Thirsty describes the sensation of needing to drink — the body’s signal that it requires water. Thirst is triggered when blood becomes slightly too concentrated or blood volume falls, detected by receptors that prompt the conscious urge to drink and the release of antidiuretic hormone to conserve water. In everyday life it follows exercise, heat, salty food, alcohol, or simply going too long without fluids. While thirst is a reliable guide for most people most of the time, it lags behind actual need during intense exertion and weakens with age, which is why the elderly are prone to dehydration. Water remains the best answer; sugary and caffeinated drinks are less effective at rehydrating.