A Review of Alternative Water Supply Systems in ASEAN

Climate change, water scarcity and pollution, and growing water demand across all sectors are stressing existing water supply systems, highlighting the need for alternative water supply (AWS) systems. AWS systems are those that have not typically existed in the traditional supply portfolio of a given service area but may be used to reduce the pressure on traditional water resources and potentially improve the system’s resilience. AWS systems have been used for decades, often where traditional systems are unable to maintain sufficient quantity and quality of water supply. Simpler forms of AWS systems, like rainwater harvesting, have been used for centuries. As human population and water demand have increased, AWS systems now play a larger role in the broader supply portfolio, but these systems alone are not able to fully resolve the increasingly complex mix of problems contributing to water stress. Entrenched challenges that go beyond technical issues include low institutional capacity for developing, operating, and maintaining AWS systems; monitoring water quality; more efficiently using available resources; and establishing clear responsibilities among governments, service providers, and property owners. Like traditional water supply systems, AWS systems should be developed within a sustainability-focused framework that incorporates scenario planning to account for evolving natural and institutional conditions. In ASEAN, the adoption of AWS systems varies among countries and provides context-specific lessons for water management around the world. This article provides an overview of AWS systems in the region, including rainwater harvesting, graywater recycling, wastewater reclamation, desalination, and stormwater harvesting.