An adequate supply of potable water to the urban poor living in informal settlements in developing countries is a serious problem, with important health and socio-social implications. Based on literature review and extensive field work, this paper evaluates the two pillars and six dimensions that limit the accessibility of potable water supply to the informal settlements in developing countries. The pillars are constituted of central actors and complementary actors; and the six dimensions are factors stratified as technical, biophysical, political, institutional, economic and social. The study identified the principles, criteria, indicators and verifiers of each factor within informal settlements in Dhaka, Bangladesh. Aggregated values of the indicators from Weighted Average (WA) and Average Ordered Weighted Average (Av-OWA) operators were used in an overall performance evaluation. It is proposed that planners and managers could make more informed decisions as a result of the model of ‘Two pillars with Six Dimensions’ to improve the present water supply situation in informal urban settlements in Bangladesh. This model can be replicated to many other informal urban settlements in developing countries, where accessibility to the formal water supply system is limited or restricted.