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. Society breaks down. Before long, 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 running out.

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

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.

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.

Some scientists think the Earth lacks the resources for many billions of people.³ As broadcaster David Attenborough says: "All our environmental problems become easier to solve with fewer people, and harder to solve with ever more people."

Others believe that population size is not the main problem. 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. We could fix them to save water.

We could limit use. The desert city Las Vegas has banned giant home swimming pools, increased recycling, removed 200 million square feet of lawns and fined those who waste water. Similar measures could work elsewhere.

Yes: The numbers tell it all. Four billion people a year - or half the world - face severe water shortages each year. And 771 million have no access to clean water. Yet our population continues to grow.

No: Forecasts are often wrong. And humans often find ways to adapt. We can carefully manage the water we have to allow it to stretch further, while looking for new solutions.

Or... Population growth drains the Earth's resources. But so do an array of other things: global warming, inequality and industrialisation. The big picture is too complex. There are no easy answers.