RDA of H20

Why is it easier to drink the recommended amount of water from certain cups, and not from others?

I have a 16 oz. insulated cup in the office from which I can suck down 2 cups of ice water in no time, three times daily. I also have a beautiful clear crackled 10 oz. glass which I love to drink from, but it takes all day to drink 20 ounces from it. But If I bring a gallon jug in, it takes me three days to finish it. Why is that? Is it all the look of the cup?