Is it added deliberately or just concentrated as a side-effect? Say fat comprised, let me guess, 5% of whole milk volume. If you take away this 5% v/v component

Is it added deliberately or just concentrated as a side-effect? Say fat comprised, let me guess, 5% of whole milk volume. If you take away this 5% v/v component, now everything else in one liter of skim milk is 5% concentrated by comparison, unless they add water.