The year is 2100 and the world is out of water. There is no water to drink, to wash with, to cool us down, to grow food and to generate energy to heat our homes. The entire planet suffers from drought. There is mass migration to the few remaining water roles. Society breaks down. ExtinctionCompletely dying out. ensues.

This could be our future. There are 326 million trillionOne thousand times bigger than a billion. gallons of water on the Earth. But only 1% of it is the freshwater we need to survive. And this stock is dwindling.

According to new data from the World Resources Institute (WRI), a quarter of the world's population already face extreme water stress.¹ This means they do not have enough water to meet basic needs.²

And the problem is getting worse. Water demand is expected to grow up to 25% by 2050. This will mean around 60% of the world's population suffer regular water stress.

The consequences could be catastrophic. The WRI's Crystal Davis says: "Water stress is climate change's deadliest and most used weapon. Water is essential to nearly every crisis we face, because when we don't have enough water, we don't produce enough food or energy. We can't keep people healthy, wildfires intensify, people migrate, conflict ensues, and equality worsens."

A big cause of water stress is the world's rising population. In 2000, this was just over six billion. Today it is eight billion. The UN estimates that it will reach 11.2 billion by 2100. As the population rises, more resources are needed. Countries use more and more water, digging deeper into their stocks.

Population worries are nothing new. In his An Essay on the Principle of Population (1798), the economist Thomas MalthusA clergyman who was interested in maths and political thought and became famous for his extremely influential work An Essay on the Principle of Population. Predictions about population growth leading to food shortages are known as "Malthusian" after him. argued that growing populations always led to poverty. In the 1960s, biologists Paul and Anne Ehrlich's bestselling book The Population Bomb (1968) predicted a global famineA widespread scarcity of food.  due to rising numbers.

Although many of their forecasts did not come true,³ many scientists echo their belief that the Earth lacks the resources to sustain many billions of people.⁴ As broadcaster David Attenborough says: "All our environmental problems become easier to solve with fewer people, and harder - and ultimately impossible - to solve with ever more people."

Others think population size is not the main problem. In his Republic, the ancient Greek philosopher PlatoOne of the most important Ancient Greek philosophers.  attacks a "luxurious city" that consumes too much. Perhaps it is how we consume that matters, not how many consume.

We waste water all the time. Every day in the United Kingdom alone, three billion litres of water are wasted - about 25% of the total use. Most of this comes from leaking pipes. Better-maintained ones would help to save water. Governments could place restrictions on use.

The desert city Las Vegas has begun "extreme" water saving measures. It has banned giant home swimming pools, increased recycling, removed 200 million square feet of ornamental grass and fined those who waste water. Similar measures could work elsewhere. We could come to understand water as a valuable resource rather than a cheap commodityA useful thing. The word has the same origin as "commode", the name of an old type of toilet..

Yes: The numbers tell it all. Four billion people a year - or half the world - face severe water shortages each year. Nearly 800 million have no access to clean water. And yet our population continues to spurt.

No: Past predictions have often proven false. And humans often find ways to adapt. We can carefully manage the resources we have to allow them to stretch further, while seeking out long-term solutions.

Or... Population growth drains the Earth's resources. But so do an array of other factors: global warming, inequality and industrialisationA period of social and economic change that transforms an agricultural society into an industrial one. . The big picture is too complex. There are no easy answers.

Extinction - Completely dying out.

Trillion - One thousand times bigger than a billion.

Thomas Malthus - A clergyman who was interested in maths and political thought and became famous for his extremely influential work An Essay on the Principle of Population. Predictions about population growth leading to food shortages are known as "Malthusian" after him.

Famine - A widespread scarcity of food. 

Plato - One of the most important Ancient Greek philosophers. 

Commodity - A useful thing. The word has the same origin as "commode", the name of an old type of toilet.

Industrialisation - A period of social and economic change that transforms an agricultural society into an industrial one.