An estimated 2.5bn people do not have access to adequate sanitation
Rapid urbanisation in developing nations threatens to trigger a water and sanitation crisis in quickly expanding slums, a report has warned.
Charity WaterAid said chronic water shortages in many of the world's slums were being exacerbated by the arrival of millions of people each week.
Populations in developing nations are set to triple over the next 30 years.
The authors called on the international community to take urgent action to tackle the problem.
"Sanitation and water are integral to urban development and yet there is no coherent commitment by governments and donors to address this crisis," said Timeyin Uwejamomere, the report's author.
"It needs to be given the highest priority and recognition that water and sanitation brings massive health, education and economic benefits."
Turning the tide
WaterAid estimates that 5,000 children around the world die each day as a result of diseases caused by unclean water and poor sanitation.
It also says that 0.8 billion people do not have access to safe drinking water, while a further 2.5 billion live in conditions lacking adequate sanitation.
"Without the aid system responding to the challenges of rapid urbanisation, the struggle against poverty is not going to be well-targeted," Mr Uwejamomere warned.
The report - Turning Slums Around - has been presented at the UN World Urban Forum, which is being held in Nanjing, China.
The gathering, the fourth of its kind, is held once every two years and brings together experts from all over the globe to discuss the challenges facing a rapidly urbanising world.
According to UN estimates, more than half of the world's population now live in urban areas and many cities in developing countries, especially African nations, are struggling to cope with the influx.
In its latest assessment, the UN-Habitat agency calculated that urban areas in these regions have grown by an average of three million people each week for the past 20 years.
The WaterAid report said that these statistics meant that it was critical for city planners to give water and sanitation services a much higher priority.
It called on national governments and urban authorities to put the issue at the centre of all urban reform strategies.
"Aid spending in the water and sanitation sector is not going to the poorest regions or countries," it stated.
"Since the mid-1990s, aid spending going to health and education has doubled; yet over the same period, the share of aid going to water and sanitation has contracted.
"Even within the aid spending that is reaching housing and urban development, it is estimated that only 1% of the budget gets to slums."
The report also quoted UN data that showed that every dollar invested in sanitation offered an equivalent return of nine dollars.
"There is no single development intervention that brings greater public health returns… to national economies in increased productivity and a reduced burden of healthcare."
The report warned delegates at the UN conference, which continues until 6 November, that the "creation of harmonious and liveable cities" was not possible with the issue being put at the heart of urban reform policies.