I carry an eastar(non BPA) type gallon jug many days. I do it when I'm trying to get a certain amount of water. If I fill the gallon jug up I know how much I've drank. Or if I'm trying to get X amount I know I need to carry the jug to the gym so I can work on at least 1 gallon of X amount. It's basically a measuring device that holds alot. I can go through 64 ounces easily depending on what's going on, and some times people don't like the taste of a certain water. For a while I didn't drink tap water and I used to fill up gallon jugs from the filtered water so it's convenience as well.