I drink milk almost exclusively instead of water, is that a problem at all?

Something I’ve wondered about, I rarely drink plain old water unless I’m desperately thirsty or it’s the only thing around (like fountains at school, when I was in school). My refreshment of choice on a hot day or just in general is milk.

I’ll usually drink a minimum of two large cups a day, however on a hot sweaty day, I can easy drink four liters of it. It’s pretty hot today, and since I’ve ran out of sprite (lol) I’m on my fourth cup in the past 30 minutes or so since I’m extremely thirsty.

Is there any issue with drinking milk instead of water, aside from the cost?