Microsoft founder Bill Gates is running a competition to reinvent the toilet for the 2.5bn people around the world who do not have access to modern sanitation.
"The current design has a real problem. It uses a lot of water, requires a very expensive system to bring in very clean water, then you make that water dirty," said Gates.
"You have a very expensive system to take it away and then you have a treatment plant and actually the water you are using there is almost ten times as much as you use for direct human consumption," he added.
The Bill and Melinda Gates foundation will provide money for scientists to develop their ideas and take them from the lab to the wider world.
To qualify for the competition the toilets must operate without running water, electricity or a septic system and must not discharge pollutants. The preferred systems will capture energy or produce other resources and operate at a cost of five US cents a day.
Chris Elias, the President of Global Development for the philanphropist's foundation, said: "What we are use to is a toilet that is connected to sewer systems and water systems, so in some ways it's a luxury to be able to flush a gallon of water every time you pull the handle on the toilet. That's not a scalable solution; most places don't have that much water."
The United Nations estimates disease caused by unsafe sanitation results in about half the hospitalisations in the developing world.