Diseases due to poor drinking-water access, unimproved sanitation, and poor hygiene practices cause 4.0% of all deaths and 5.7% of all disability or ill health in the world. About 80% of urban dwellers have access to piped drinking water and 96% have access to improved drinking water sources. However, often the bacteriological quality of this water remains poor; more than 50% of urban residents in developing countries are still affected at one time or another by diseases related to insufficient access to safe drinking-water and improved sanitation.
Contaminated drinking-water is estimated to cause more than 500 000 diarrhoeal deaths each year. Contaminated water can transmit diseases such as diarrhoea, cholera, dysentery, typhoid and polio. Health costs associated with waterborne diseases such as malaria, diarrhoea, and worm infections represent more than one third of the income of poor households in sub-Saharan Africa.
Health risks are often exacerbated by poor sanitation. Some 20% of the urban population still lacked access to improved sanitation in 2012 and 100 million city dwellers still practiced open defecation – although gains in access to improved sanitation have generally been much more rapid in cities than in rural areas over the past two decades.
Urban solid waste disposal is another sanitation-related challenge. Recent estimates also suggest that cities generate 1.3 billion tonnes of solid waste per year, a figure expected to rise to 2.2 billion tonnes by 2025. Failure to adequately collect and dispose of solid waste presents can increase the proliferation of disease-carrying vectors, such as rodents and insects. These risks can be exacerbated by other urban conditions, such as overcrowding.
Social inequities in cities play an important role in water and sanitation-related risks – with informal settlements and slums generally having lower levels of access than other parts of the city. Due to crowding and other factors, slums can thus become a nexus for water and sanitation-related infectious disease transmission.
Slums and other dense, informal urban neighbourhoods pose challenges for improving sanitation provision insofar as sewer systems will likely be required, but also costly to install within established and densely-populated neighbourhoods. Urban sprawl also makes sewage infrastructure more costly to install and energy intensive to operate – as compared to planned, compact development where infrastructure is built in advance and gravity flow can be used to pump sewage downhill. Some studies (e.g. in South Africa) tested safe, low-cost, on-site biological sewage treatment in urban residential settings.