By the turn of the century, half the 6.2 billion population of the planet will be urban. The unplanned and often chaotic growth of mega-cities will mean that at least half of their inhabitants will live in crowded tenements, shanty towns and slums without basis amenities. Overcrowding, filth and squalor encourages the spread of infectious diseases and poses massive threats to urban health. Even in the developed world, ill health as a consequence of urban living is prevalent.
The lack of adequate solid waste disposal and sewerage services causes serious public health problems in many cities, causing many diseases including often-fatal water-borne diseases such as cholera and dysentery.