Massive slums have become major features of cities in many low-income and middle-income countries. Here, in the fi rst in a Series of two papers, we discuss why slums are unhealthy places with especially high risks of infection and injury. We show that children are especially vulnerable, and that the combination of malnutrition and recurrent diarrhoea leads to stunted growth and longer-term eff ects on cognitive development. We fi nd that the scientifi c literature on slum health is underdeveloped in comparison to urban health, and poverty and health.

It is fitting that the United Nations Habitat III conference in October will be held in Quito, Ecuador. In April, the city and nearby Portoviejo and Manta suffered an earthquake that killed more than 660 people and injured at least 10,000. Around 73,000 people were displaced. Some 700,000 needed emergency assistance, such as drinking water, sanitation and hygiene kits. Many water-supply systems and hospitals were destroyed or disrupted. Insurance companies estimated the damage at US$2.5 billion, of which only 16% was insured.

Many of the world’s megacities depend on groundwater from geologically complex aquifers that are over-exploited and threatened by contamination. Here, using the example of Dhaka, Bangladesh, we illustrate how interactions between aquifer heterogeneity and groundwater exploitation jeopardize groundwater resources regionally. Groundwater pumping in Dhaka has caused large-scale drawdown that extends into outlying areas where arsenic-contaminated shallow groundwater is pervasive and has potential to migrate downward.