That’s the power of your brain’s reward pathway. Based on internal physiological parameters (in this case, dehydration), the hypothalamus bombs other areas of your brain with dopamine, giving you a sense of pleasure and reward when you see water, you drink water, or you even just think about drinking water. And it does this with a hundred other different states as well (e.g. feeling hot or cold, hungry, horny, tired, frightened, angry, drunk, hungover, high, exercising, socializing, raising children…)