One of the richest men in the world is looking for a more efficient way to get rid of body waste.
At the Reinvent the Toilet fair at the Microsoft campus in Seattle this week, contestants showed off new toilet designs, including ones that used microwave energy to turn excrement into electricity.
Another even used urine to flush solid waste and turned solid wastes in charcoal.
The winning design by Prof Michael Hoffman used solar power and generated hydrogen gas and electricity.
A team from London made a toilet that used black soldier fly larvae to process solid wasted. It is already being field tested in South Africa.
Traditional toilets waste precious drinking water and are impractical in parts of the developing world.
1.5 million children die each year from diarrhoeal disease, and Gates has committed $370 million to test out new toilets within three years.