Kittens naturally drink their mothers milk for the first few weeks of their lives. After that, they can start to be weaned onto solid food and water. Kittens do not need cat milk added to their diet to stay healthy as this is just extra calories thatll make them put on a lot of weight. In fact, cows milk or any sort of human milk substitute can make them really sick. It is important to provide clean, fresh drinking water at all times. Wet food can also help kittens get enough water in their diet, as it contains a lot of moisture.