Well, you don't always have a water bottle and a place to fill it up from. That said, I agree that general societal pressure to reduce the number of pint/quart-size throwaway bottles is desirable in the same vein as reducing the use of throwaway plastic grocery bags. At the same time, given the choice between people buying bottles of water and bottles of soda, the former counts as progress in general and I'm not sure we want to discourage it.