Worldwide, 2.5 billion people lack access to adequate sanitation, and an unsettling 1 billion still practice open defecation--which means they do their business where they can. When you account for the economics of this, the numbers are staggering. The World Bank says a lack of toilets costs $260 billion annually in health and societal impacts.
To put these numbers into context, the bank has produced the graphic below. It breaks down the regions most in need of improved sanitation (Sub-Saharan Africa and South Asia), and which places bear the greatest economic cost. East Asia comes out worst ($80 billion a year) followed by South Asia ($60 billion). India alone has a $54 billion shortfall from bad toilet systems, with health impacts contributing most to that. Diarrheal disease causes 1.4 million preventable deaths a year, stunts child growth, and lowers productivity, for example.
The good news is that cheap fixes can pay big dividends. The bank estimates that every dollar invested in countries like Indonesia and Kenya has had more than five-fold return. That's mainly from increased tourism, improved safety, higher land value, and better water supplies. Oh, and greater dignity for people.
The bank has calculated the cost and affordability of sanitation techniques, such as pit latrines (see here). Improving conditions doesn't mean simply exporting Western-style technology. Having said that, nonprofits like the Bill and Melinda Gates Foundation have funded several ingenious (and cheap) toilet ideas for the developing, as we covered here.