On a civic scale, health brings wealth. And no society can be healthy without the proper disposal of human waste. The filthy fact is that what might seem like common convenience to many folks in developed areas is still out of reach for a significant portion of Earth's residents. The World Health Organization predicts that in four years 2.7 billion people around the globe will still lack access to basic sanitation. Diseases transmitted via contaminated water include diarrhea, cholera, dysentery, typhoid and hepatitis A. Worldwide, diarrheal diseases are the second leading cause of death—after pneumonia—for children under the age of five.

Most of those deaths could be avoided with proper sanitation. Many people have a basic understanding about how to dispose of their waste, but poverty, politics and prejudice often get in the way.

The improvement of functional and effective sanitation has been a largely unsung force for development and infrastructure in the rise of cities throughout history. And it starts with a toilet that's more than a hole in the ground.

» View a slide show of the history of the toilet