The Southeast Asian environment has been degraded by the release of industrial and domestic wastes, agricultural and aquacultural chemicals, and pollutants from automobiles. It suffers from water-related disasters, Tsunami, floods, typhoons, etc. In order to deal with these issues an integrated approach from the inhabitants, governments and researchers is essential.The environmental threats arising from the increasing population, overuse of natural resources, industrialization, urbanization, and natural disasters present ever increasing challenges to pursuing sustainable development of the region. Many developed countries such as Japan have experiences of dealing with severe environmental pollution and this publication is the result of building an academic network among researchers of related fields from different regions to exchange information.The most important articles presented at the Fourth and Fifth International Symposiums on Southeast Asian Water Environment have been selected for this book.This book will be an invaluable source of information for all those concerned with achieving global sustainability within the water environment in developing regions, including researchers, policy makers, NGOs and NPOs.