The percentage of casein protein in cow's milk is higher than that in human milk because a calf has greater nutritional needs than a human baby - its growth rate is about twice that of its human counterpart. Because its casein content is higher, cow's milk is harder to digest than human milk.
If the milk weren't stretched with water and the baby's intake of the milk (and its casein) thereby reduced, it would put a strain on the baby's delicate digestive system.
Sugar is added to the cow's milk to make the infant's formula taste more like human milk, which is naturally sweeter. Speaking of sugar, a parent should not let a baby get into the habit of falling asleep with a milk bottle. This beverage (as well as sugary fruit juices) is laden with bacteria that can cause tooth decay. If a parent feels the child needs a nightcap, the bottle crutch should contain plain water.
** Asian Cooking **