The Clean Development Mechanism (CDM) provides industrialized countries with an incentive to invest in emission reduction projects in developing Countries to achieve a reduction in CO2 emissions at lowest cost that also promotes sustainable development in the host country. Solar water heating systems (SWHs) could be of interest under the CDM because they directly displace greenhouse gas emissions while contributing to sustainable development by reducing local pollutants. However, there are only three solar water heating projects under the CDM so far. An attempt has been made to estimate the CDM potential of SWHs in India in this study. Our estimates indicate that there is a vast theoretical potential of CO2 mitigation by the use of SWHs in India. The annual CER potential of SWs in India could theoretically reach 27 million tonnes. Under more realistic assumptions about diffusion of SWHs based on past experiences with the government-run programmes, annual CER volumes by 2012 could reach 4-9 million and 15-22 million by 2020. This would require that the government sets the subsidy level for SWHs at a level that allows them to become viable with the CER revenue. From a macro-economic point of view this makes sense if the sustainability benefits are deemed sufficiently high to warrant promotion of this project type. (c) 2008 Elsevier Ltd. All rights reserved.