1. Woods Institute for the Environment, Stanford University, Stanford, California 94305, United States
2. Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, North Carolina 27695, United States
3. Department of Civil and Environmental Engineering, Tufts University, Medford, Massachusetts 02155, United States
4. Program in International Community Nutrition, University of California, Davis, California 95616, United States
5. International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka 1000, Bangladesh
6. Department of Civil and Environmental Engineering, Stanford University, Stanford, California 94305, United States