1. School of Environment, Resources and Development, Asian Institute of Technology, P.O. Box 4 Klong Laung, Pathumthani 12120, Thailand (E-mail: thamarat@ait.ac.th)
2. Department for Water and Sanitation in Developing Countries, Swiss Federal Institute for Environmental Science and Technology, P.O. Box 611, CH-8600 Duebendorf, Switzerland (E-mail: doulaye.kone@eawag.ch)