Why is bargaining more common in poor countries?
In first world countries, the price of a bottle of water is set by a well-established market. There are millions of prospective buyers of a bottle of water and thousands of prospective suppliers, and while many suppliers are able to achieve brand differentiation, for the most part their water is fungible. Moreover, the supply and demand curves of water are reasonably stable, and water companies have the excess capital to hold inventory stockpiles that further reduce the volatility of prices. There is little information asymmetry. Customers can easily comparison shop, and price discrimination is very difficult. Suppliers are generally large corporations, which means that allowing bargaining would introduce massive headaches, such as agent-principal issues. There's also a feedback effect: once an economy and culture are built around fixed prices, it's more difficult to introduce bargaining. Water companies are in a low-margin business where their money comes from high volume. Spending resources bargaining would destroy those margins.