I lived in Honduras and the situation was happening there. You can't drink the tap water. Everybody knows it. So there is a huge business in selling water to people. And that business relies on plastic because for what it does, plastic is much lighter than glass or metal containers. Much lighter. That means trucks can carry a lot more liquid with the same fuel. Glass and metal containers might be easier to reuse or recycle, but you have to factor in the climate impact of the fuel used by the trucks hauling the liquid.

I suppose the best climate impact would be to support municipal water systems worldwide and not put the blame on consumers who don't have any good choices.