We have a filter at work and a filter at home and knowing the environmental impact of those stupid bottles, I just refill a reusable water bottle with my "free" filtered water when I am going out.
I also am a bit of a conspiracy theorist when it comes to those bottles of water. Since so many of them are from muni. water supplies, I think it was a bit of Emperor's New Clothes, or a way for Coca-cola/Pepsi to get the non-soda drinker to buy their products.