The report on Market Opportunities for Decentralised Wastewater Treatment Systems (DEWATS) in South-East Asia (SEA) is prepared within the frame of the joint project of ESCAP and UN-Habitat on “Strengthening capacity of policymakers in SEA to promote policies and developing plans for improved wastewater treatment and reuse in urban and peri-urban areas”, to address the fast-growing problem of untreated wastewater through promotion of the Decentralized Wastewater Treatment Systems (DEWATS) in 2013-2015.