"No one wants to be the rock star for diarrhea," says Mikkel Vestergaard Frandsen, Danish inventor of the LifeStraw, a $4 drinking tube that removes almost all the disease-causing bacteria, viruses, and parasites in untreated water.

It’s a provocative statement aimed squarely at celebrities like Bono, who have lined up behind AIDS, while unglamorous diarrhea continues to be one of the most persistent and pervasive health disasters in the developing world. According to the World Health Organization, diarrhea kills 6,000 people daily, most of them children under the age of five.

The LifeStraw, which has drawn praise from former president Jimmy Carter, economist Jeffrey Sachs, and singer Peter Gabriel, is clean water’s celebrity product. Since 2005, aid groups in sub-Saharan Africa, Asia, and Latin America have distributed hundreds of thousands of the bright blue purifiers, which house fine mesh, iodine beads, and active carbon and can be used anywhere to suck up surface water and transform it into drinking water. Each lasts roughly one year. In February, Vestergaard Frandsen intro­duced LifeStraw Family, a $15 water-purification filter that has already outsold the LifeStraw four times over, providing more than a million families with water that meets E.P.A. standards.

Vestergaard Frandsen, 35, didn’t intend to become a humanitarian entrepreneur. His family’s business once manufactured hotel uniforms. But he fell for Africa as a teen, and when handed the keys to the eponymous firm at age 21, he set about devising tools to combat malaria-carrying mosquitoes and waterborne diseases. His first product? Insecticide-laced mosquito nets that go for $5 a throw. The company will sell its 150 millionth net this summer.