Water is one of our most important resources. Water moves in the Water Cycle. How much you have in any area usually depends on how much rain falls or snow melts. But when water reaches rivers it can be taken from an area of plenty to an area of shortage. Some people live in areas where it doesn't rain very much, but they have large rivers running nearby. The Nile (for Egypt) and Colorado (for Arizona/Nevada/California) are rivers that do this.

Not all water is found on the surface. A lot of water that seeps into the ground goes through the soil and into rocks below. Much of it remains there, and can be reached by wells.

The point is, that there is a certain amount of water that is available to us, and it varies from place to place. Those people who live in areas where it rains evenly though the year are best off. Those areas where it only rains in part of the year have to think about how to store water from a season of plenty to cope with a season of shortage. They do this with big dams and by using wells. Those who have very little rain at any time of year are usually also those where the rain is least reliable. This makes living in such areas especially difficult. The area of Africa on the Equator-side of the deserts are like this (called sub-Saharan Africa).

As you know, the world's population is still rising fast. This means more people want water to drink. So places that had sufficient water in the past, many not have sufficient now. They may have to try to get water from unsafe sources, such as polluted rivers or rivers where microbes can cause disease.

It is likely that shortage of water will be a bigger and bigger problem in the future. Some people have predicted that wars will happen as countries try to get a bigger share of the world's water.