According to the United Nations Human Settlements Programme (UN-Habitat), 924 million people lived in slums in 2001. Population growth in these settlements is much greater than in other urban areas. The estimates suggest that this figure may rise to 1.5 billion by 2020 (Payne, 2005). This rapid increase is expected despite “slum upgrading” efforts that have been taking place for decades, though inconsistently and with disruptions over time. There is a prolific literature on informal settlement areas, but research on access to essential services such as water and sanitation (WS) in these areas is very limited. Most studies consider issues of access in connection to urban poverty, an approach that often reduces the discussion to the income and expenditure constraints faced by households. Examining access to WS in the slums spurs an appreciation of the multidimensional nature of the problem, including income poverty, infrastructural limitations, asset ownership and housing quality. Moreover, developments in the slums concern every aspect of the Millennium Development Goals (MDGs).

Living conditions in slums vary not only from one country to another but also from one settlement to another within the same country. Some countries classify slums in different ways to distinguish those with greater deprivation in terms of urban living standards. For example, the terms favelas, loteamentos, invasões and cortiços describe in descending order Brazilian slums with greater to lesser urban development. In Buenos Aires, asentamientos are considered to be proper slums whereas villas are squatter settlements that have undergone some process of urban development and consolidation. Similarly in Sri Lanka, labour lines, unserviced urban neighbourhoods and shanties all refer to different categories of slums.