Cow's milk is about 87% water.

Bovine milk typically contains 87.3% water and 12.7% solids. These solids include 3.9% fat and 8.8% other materials like protein and minerals. The most common proteins are casein and whey. Lactose is the main sugar in milk and provides energy.Water acts as a base that holds all these ingredients together. Fat exists as tiny droplets floating in the water. Casein proteins form small clusters called micelles. These clusters stay spread out in the water so the milk does not clump together.The cow's mammary glands control this balance using osmotic pressure. This process ensures the milk has the right thickness. If there were less water, the milk would turn into a thick paste. Calves would not be able to drink it.The exact amounts of water and fat can change depending on the cow's breed and what it eats. For example, Jersey cows often produce milk with more fat than Holstein cows. However, the water content always stays close to 87% to keep the milk stable.