The Earth's water reserves are abundant, totaling a staggering 1.45 billion cubic kilometers. Despite the enormous amount of water on the planet, very little of it can be used directly by people for production and living.

Firstly, seawater is salty and bitter, not drinkable, not waterable, and difficult to use for industry. Secondly, the Earth's freshwater resources account for only 2.5% of its total water volume, and of this tiny amount, more than 70% is frozen in the ice caps of the Antarctic and Arctic, and with the difficult-to-use mountain glaciers and permafrost, 87% of freshwater resources are difficult to use.

The only freshwater resources available to humans are rivers, lakes, and groundwater, which account for 0.26% of the Earth's total water. Global freshwater resources are not only in short supply but are also very unevenly distributed across regions.

By region, nine countries - Brazil, Canada, China, the United States, Indonesia, India, Colombia, and the Congo - account for 60% of the world's freshwater resources. Some 1.5 billion people in 80 countries and territories, representing about 40% of the world's total population, have insufficient fresh water, with some 300 million people in 26 of these countries suffering from extreme water shortages.

What is even more frightening is that by 2025, it is expected that 3 billion people in the world will face water shortages and 40 countries and regions will have severe freshwater shortages.

The highly uneven distribution of freshwater resources has led to severe water shortages in some countries and regions. For example, the Zaire River in Africa, which accounts for 30% of the continent's renewable water supply, flows mainly through sparsely populated areas, resulting in severe water shortages in some highly populated areas.

The Amazon River in the Americas, for example, accounts for 60% of the total runoff in South America, but it too does not flow through densely populated areas and its abundant water resources cannot be fully utilized.

Central Asia face a similar situation, with abundant water resources flowing through Siberia and into the Arctic Ocean, while the populous western, southern and central Asian regions suffer from water shortages.

The global distribution of water resources is largely geographically determined and difficult to redistribute. Nine countries - Brazil, China, Canada, Indonesia, the United States, India, Colombia and Zaire - hold 60% of the world's water resources, and the cost of redistribution, even at a certain scale, would be extremely high.

Water is an irreplaceable resource. Finding an ideal alternative to water is much more difficult than finding alternatives to resources such as oil and wood, and although many water-scarce countries have started desalination efforts, they are currently far from being able to solve the water shortage, both financially and technologically.

Water scarcity is divided into two main areas: resource-based and water-quality scarcity. Resource-based scarcity is mainly due to the geographical differences in the distribution of water resources, resulting in a shortage of water in local areas due to the distribution of water.