Survival requires regulation of water and salt content. Loss of fluid from cellular or extracellular triggers drinking. However, a palatable taste can override homeostasis. A satiety signal is generated by oral and gastric factors in combination with absorption from the gut. Specialized cells in the brain (‘osmoreceptors’) detect hydration of the extracellular fluid. Other receptors are sensitive to blood volume. In addition to incentive motivation, there appears to be a negative reinforcement from the aversiveness of dehydration. Feeding and drinking interact. Dehydration causes a reduction in the amount of food ingested. Food intake can influence water intake. If hungry but not thirsty rats are given small food pellets at, say, every 90 seconds, they drink very large amounts of fluid: ‘schedule-induced polydipsia’. Sodium appetite is associated with hedonic hotspots. Potassium appetite relies upon a learned association between the taste of a food and restoration of potassium levels.