After five years of making grants to help the developing world deal with water, sanitation, and hygiene issues, the Bill & Melinda Gates Foundation announced today that it will narrow its focus to sanitation.

Sylvia Mathews Burwell, who leads the Seattle foundation’s global-development program, made the announcement at a conference on sanitation in Kigali, Rwanda.

Gates anticipates spending the same amount—roughly $40-million per year—on sanitation as it has been giving to date in the three areas combined.

In calling on the world to help “reinvent the toilet” for the 21st century, foundation leaders said they were putting more money into sanitation because such projects have been neglected by other donors.

Frank Rijsberman, the philanthropy’s director of water, sanitation, and hygiene, said he estimates that donors and governments devote nine times as much attention to water issues as they do to sanitation. Meanwhile, United Nations figures suggest that the world has made far less progress toward expanding access to sanitation than it has toward providing clean drinking water.

“We’ve decided to flip that and say we’ll focus 90 percent of our attention on sanitation,” Mr. Rijsberman said in an interview.

Nearly half of Gates’s sanitation grants will support new approaches to disposing of human waste. Another 45 to 50 percent will help communities put sanitation services into effect, while 5 to 10 percent will support advocacy efforts.

Mr. Rijsberman said a focus on innovation was important because the flush toilet hasn’t been significantly updated since the 19th century.

Rich countries have little incentive to support new approaches to waste disposal because existing systems work well for them, he said. But U.N. estimates suggest that half the people in developing nations don’t have access to sanitation.

“For the same reason that Bill Gates said we need to look at these neglected tropical diseases because no one invests in them, we’re saying no one invests in toilets that actually work for poor people,” said Mr. Rijsberman.

At the conference in Kigali, the Gates foundation announced $42-million in new grants to support innovation and other sanitation work. Eight universities won grants totaling $3-million for efforts to design toilets as stand-alone units that don’t need sewer systems or electricity to dispose of waste.

Mr. Rijsberman said the Gates fund might support a handful of new water projects in the future, but the emphasis would be almost entirely on sanitation.