My Audi Q5 and Subaru Outback both have door pockets shaped for a water bottle. These spaces are large enough to carry store-bought or re-usable (Nalgene type) water bottle up to 40 ounces. The Outback has these spaces in all four doors. We use these water bottle holders all the time when we're out hiking and biking, and were a little disappointed to find that our new C Max doesn't have anything similar. It doesn't seem like it would add significantly to the cost of producing a door panel, but adds a lot of convenience.