Another problem postulated to me is the lack of food and water for many of the world's poor. I think I already discussed food.
In many impoverished countries, not only is food pricey for many of its citizens, but clean water is not readily available at prices less than 1st world bottled water (which is a fortune as far as they are concerned.) They get water, but it's scummy river water and needs extensive sterilization, lest they get sick. And sometimes, they don't do it right, either because they forgot, are in a hurry, or the water seems fine at first. (The water could be perfectly clear and clean smelling, but still riddled with bacteria.)
Much of this is in Africa, which has mostly murky, unwise-to-drink-from rivers. I propose an inter-African water-pipe system, with filtering plants in the uninhabited desert part. Yes, water treatment plants do tend to smell, but why not stink up the places where nobody goes anyway?
Another part of the problem is political in nature: water bottling pays the local governments for the water better than all the peasants could, even collectively. Sometimes a government really needs to do what is best for its people, rather than what's best for its wallet. And unfortunately, sometimes a local government doesn't.
Some researchers are working on a cheap, portable, water sterilizer for those regions where the government doesn't. They've almost got it. Almost.