@KoiwiGal - One of the reasons Edwin Chadwick wanted to reform and centralize sanitation was because he thought it would save money in the long run.
And he is probably right. While people argue about having a "nanny state" in reality public health concerns can have a lot of impact on a wide range of people who didn't necessarily contribute to the problem.
A similar example is smoking. Second hand smoke can cause health problems in people who don't smoke, and drive up insurance premiums and use up health care and so on. Which is why smoking in public places like restaurants is mostly banned now.
The same thinking can be applied to the developing world. It would cost a lot less to put in permanent sewers than to continually fight the malaria that results from standing water.
The trouble is finding the funds to do either of those things.