Curses!
(I never look at the posting times & dates…)
There is so much that goes into an answer to this, it’s hard to know where to start. If someone has no first-hand working knowledge of the world’s less-agreeable spots or the incredibly brutal existence led there, then I’m not sure the answers will make much sense anyway.
It’s been pointed out that in many instances the water source is hopelessly contaminated. This is not always the result of fecal contamination that results in cholera and dysentery, but is also the result of shallow water sources that breed other unpleasantness such as Guinea worm.
The idea of chlorination is not quite the same sort of suggestion as “move to where the food is”, but may be just as unrealistic for communities that have no access to most western consumer goods, nor the wherewithal to purchase them.
There have been many well-meaning aid projects in places like Africa, such as the drilling of wells, all accompanied by much hoopla and press releases. Unfortunately, the practice in the past has been to drill the well, neglect to train someone in the maintenance of said well, and not provide any repair parts to keep it running. Once the thing breaks, it’s back to hauling water from whatever polluted source has been traditionally used for centuries.
So that’s a start on the topic. Someone else can carry on.