About one on four child on the planet will die, have their growth stunted or otherwise suffer from a lack of water by 2040, Unicef has warned in a new report.

Thirsting for a Future, released on World Water Day, paints a bleak picture of the next few decades in which the rising global population, a surge in demand for water, rising sea levels and increasingly common droughts combine to create a crisis of epic proportions.

Already 36 countries in the world face “extremely high levels of water stress”, the report by the UN children’s agency said.

Every day more than 800 children under five die from diarrhoea linked to a lack of clean water and poor sanitation.

UNICEF - World Water Day 2017, Thirsting for a Future Show all 9 1 /9 UNICEF - World Water Day 2017, Thirsting for a Future UNICEF - World Water Day 2017, Thirsting for a Future United Nations Headquarters Getrude Clement, a 16-year-old radio reporter from Tanzania and UNICEF climate advocate Unicef UNICEF - World Water Day 2017, Thirsting for a Future Fiji Girls from Nakorovou village in Vuna on Taweuni Island, helping their mothers with laundry on a shore of their destroyed village Unicef UNICEF - World Water Day 2017, Thirsting for a Future Haiti Hurricane Matthew passed over Haiti, with heavy rains and winds Unicef UNICEF - World Water Day 2017, Thirsting for a Future Bangladesh Students make their way to school after heavy floods in Sariakandi Upazila, Bogra, Bangladesh Unicef UNICEF - World Water Day 2017, Thirsting for a Future Alaska An Iñupiat girl Amaia, 11, standing on a ice floe on a shore of the Arctic Ocean in Barrow, Alaska in the United States of America Unicef UNICEF - World Water Day 2017, Thirsting for a Future Nigeria A girl pumps water from a borehole provided by UNICEF in Old Maiduguri, Borno State, Nigeria Unicef UNICEF - World Water Day 2017, Thirsting for a Future Kiribati A boy walks from school to his house in Aberao village in South Tarawa, Kiribati. Kiribati is one of the countries most affected by sea level rise Unicef UNICEF - World Water Day 2017, Thirsting for a Future Zimbabwe Siyephi Village, Bullilima District in Matebeland Unicef UNICEF - World Water Day 2017, Thirsting for a Future Myanmar Fourth-grade students from Hnen Ser Kyin Middle School wash their hands at a community water point in the village of Hnen Ser Kyin, Magway Region Unicef

The same conditions have resulted in an astonishing 156 million children under five suffering from stunted growth, which causes irreversible physical and mental damage.

In a foreword to the report, Professor Anthony Lake, executive director of Unicef, wrote: “Water is elemental. Without it, nothing can grow. And without safe water, children may not survive.

“Children without access to safe water are more likely to die in infancy – and throughout childhood – from diseases caused by water-borne bacteria, to which their small bodies are more vulnerable.

“When these diseases don’t kill outright, they can contribute to the stunting of children’s bodies and minds – and the blighting of their futures – by undermining their ability to absorb nutrients.

“When a community’s water supply dries up or becomes contaminated – because of drought, because of flooding, because of conflicts that undermine infrastructure and prevent people from reaching safe water sources – such diseases abound.”

Parts of Africa and the Middle East are currently in the grip of a serve drought.

“We see the terrible effects of water scarcity today all over the world – and nowhere more tragically than in parts of Nigeria, Somalia, South Sudan and Yemen, where drought conditions and conflict are producing deadly effects,” Professor Lake said.

“Nearly 1.4 million children face imminent risk of death from severe acute malnutrition as famine grows in these areas.

“In Ethiopia alone, we anticipate that more than nine million people will be without safe drinking water in 2017."

The increasing population and rising demand means the amount of water available to each person on the planet cut by 50 per cent by 2050, the report warned.

But as global warming will result in higher rates of evaporation and less rainfall in many areas – such as the Middle East – “water will become even scarcer”, it added.

“Rising temperatures increase the atmosphere’s water storage capacity, which essentially reduces water availability on the ground, particularly during the warmer months of the year,” it said.

“Then, when the air eventually cools, more intense rainfall occurs, this can lead to increased frequency and intensity of tropical cyclones and other extreme weather events. Rising temperatures also impact water by creating an environment for bacteria, protozoa and algae to grow, which can lead to illness and death in children.”

Higher sea levels can contaminate freshwater with salt, rendering it undrinkable. Low-lying areas and small islands, the places most affected by this problem, are home to about 25 per cent of the world’s population.

"The changing climate is one of many forces contributing to an unfolding water crisis. In the coming years, demand for water will increase as populations grow and move, industries develop and consumption increases," the report said.

"This can lead to water stress, as increasing demand and use of water strains available supplies. By 2040, almost 600 million children [one in four of the total] are projected to be living in areas of extremely high water stress. If action is not taken to plan for water stress, and to safeguard access to safe water and sanitation, many of these children will face a higher risk of death, disease, and malnutrition."

But Unicef stressed that a “growing water crisis” was “not inevitable, if we act now”.

It said countries should prioritise access to safe water for the most vulnerable children; increase the capacity of water storage facilities; factor in climate risks to water and sanitation policies; and get businesses to work with communities to prevent contamination and depletion of clean water supplies.

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“In a changing climate, we must change the way we work to reach those who are most vulnerable,” Professor Lake said.