I have a 6 person household, we go through like a gallon a day I swear, but it's all being drank by my mom's boyfriend. Before he moved in a gallon could last us a week and a half.
me and one of my siblings are the only one that drinks our milk (oat/ almond milk usually) and it takes us a while to drink it all, it's not a gallon either, it's much less
Funny thing, actually: I don't even drink milk. Milk actually makes my right ear itch and my toenails start to grow a little faster. I don't even want to go in to what water does to me! lol