It's a very real issue. The main problem is that Coca Cola basically took over the whole country. In my experience you can't find a dinner table without a liter bottle of coke or processed juice. I've gotten strange reactions when asking for water, it's just not done most of the time. The other factor is that because they (and Nestlé I think) use up so much of the water supply to produce their drinks in the first place, it drives up the price of water in those areas to such an extent that you "might as well" just buy soda.