By the same year, he said, 2.5 million people will lack access to improved sanitation. Human waste and garbage poses a health risk in those areas, he said.
That issue is most dire in rural areas, said Christine Moe, director of the Center for Global Safe Water at Emory University, in Atlanta. Historically, Moe said, urban populations have been more likely to have basic sanitation services and clean water than people in rural areas. So most nongovernmental organizations focus their efforts on improving conditions in rural areas, she said.
All the while, she said, a global population shift has made the issue more complex. The global population is becoming increasingly urban, she said; in 2008, more people in the world lived in cities than rural areas, and that urbanization continues to grow.
Projections show that most of the world's urban growth over the next 30 years will occur in developing countries. Although urban areas have historically had better access to clean water and sanitation, she said, urban population growth could outpace governments' ability to keep up with water needs.