An estimated 800 million urban dwellers lack access to safe and adequate drinking water. Most of those people live in unplanned, low-income areas and slums. The vital role of groundwater for this group remains largely unexplored despite that some 50 per cent of all urban water use worldwide is attributed to well, spring and borehole sources. None of these numbers have been broken down to show whether and how the dependency on groundwater is divided between rich and poor, however. There are reasons to believe that people living in informal settlements and slums resort to using groundwater to a larger degree than those connected to public utilities’ water supply networks. ~~This review seeks to shed light on why and to what extent people in urban poor areas use groundwater for drinking and other domestic purposes; strategies employed to access the water; the implications of the dependence on groundwater; and what this should mean in terms of policy and regulation. It contains two case studies – of the cities of Bangalore, India, and Lusaka, Zambia – in order to substantiate the limited amount of statistics and literature in the field.