World Toilet Day is November 19, and a reminder that substandard sanitation affects billions of people.
Some 13 percent of humanity lives without any toilets, and 25 percent have only pit latrines or something similar.
The poor sanitation adds up to enormous dangers to human health from multitudinous untreated microorganisms.
Even developed countries such as Australia and the United States are not immune to the problem.
A 2012 challenge from the Bill & Melinda Gates Foundation resulted in a new generation of inexpensive, off-the-grid toilets.
Researchers developed systems that recycle urine and feces into energy and fertilizer, and that take into account the diverse ways that humans use the toilet around the world.
South Africa, meanwhile, has pioneered community toilets in areas where installing complete in-home sanitation systems in impoverished neighborhoods is out of the question.
Though failures abound, a new toilet-engineering challenge sponsored by the Georgia Institute of Technology aims to spur even more innovation.