Water is the most important nutrient of all and essential for life. Animals can lose almost all their fat and half their protein and still survive, but if they lose 15% of their water, it will mean death.

The amount of water an animal should consume per day is roughly equivalent to its daily energy intake in kilocalories. This means that a healthy dog or cat would normally need around 50 ml per kg bodyweight per day; e.g., 200 ml for a 4 kg cat.