Bill Gates wants to reinvent the toilet for over 2 billion people who lack access to clean water.

His foundation, the Bill and Melinda Gates Foundation, has backed a waterless toilet, called The Nano Membrane Toilet.

Gates hopes to install the toilet in poor urban areas - before he scales it out to rural areas.

Bill Gates is on a mission to reinvent the way huge swaths of the world's population go to the bathroom.

And he credits his time at the helm of Microsoft for giving him the "bullheadedness" to do it, according to a recent interview with psychologist Steven Pinker in The New York Times.

Through his foundation, the Bill and Melinda Gates Foundation, Gates is funding cheap, waterless toilets, designed to serve poor urban areas in countries that lack consistent access to clean water and sanitation. More than 2.4 billion people around the world still live in unsanitary conditions, putting them at risk for diseases, according to some estimates.

"We want to reinvent the toilet so it doesn't need water piped in or out - just a chemical process, so that even Indian cities that will never spend $1 billion can have a toilet as good as a Western one," Gates said in the interview. "This is a 10-year quest."

According to the Center for Disease Control, 88% of deaths worldwide due to diarrheal disease can be attributed to unsafe water, poor hygiene, and inadequate sanitation. And these diseases are the second highest cause of death for children under 5, killing more children than AIDS, malaria, and measles combined, according to the CDC.

Through his foundation's "Reinvent the Toilet Challenge," Gates has given millions to teams seeking to develop waterless toilets in the last several years. To be entered into the challenge, toilets had to cost less than 5 cents a day to operate, without the need for external electricity or running water.

In 2011, the first year of the challenge, Gates awarded the top prize to the California Institute of Technology's prototype of a self-contained, solar-powered toilet. The toilet produces enough energy to run an electric reactor that can break down human waste and produce hydrogen, according to Gates' blog. Among the other finalists: A toilet developed at the University of Toronto that combusts waste with ultra-violet light, and a toilet developed at a university in the United Kingdom that transforms fecal matter into a "biological charcoal," which can be used as fertilizer or even a fuel source.

Each of the finalists received a $400,000 grant from the Gates Foundation to continue improving their prototypes.

Seven years later, Gates is testing more prototypes in poor, urban communities in India and across Africa. He recently awarded a $7 million grant to a toilet developed by two Duke University professors, and he gave Duke $3.7 million to establish a new Sanitation Technology cluster, focusing on interdisciplinary research into toilets, according to Inside Philanthropy.

And, in 2012, Gates sank $710,000 into a toilet developed at Cranfield University, called The Nano Membrane Toilet. That toilet - which received another substantial grant at the end of 2016, is now being field tested in Ghana.

Here's how the toilet works: