No, not quite. Lactose is much thicker than water and doesn't do much to flush impurities out of your organs, like pure water does. Drink both (the calcium in the milk will help strengthen your teeth), but don't count the milk as part of your MDR (Minimum Daily Requirement) water intake. Think of the water as (among other things), keeping your internal filters from getting clogged up with crud. It also hydrates your skin and keeps it supple, which will slow the aging and wrinkling processes, which you might not think is important now, but you can't start too early.