4.3 Water Supply

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1. Rivers

A river is a natural flow of fresh water that moves across the land and usually empties into a sea, lake, or another river.

• Rivers collect water from rainfall and from melting snow or ice in mountains.
• People have used rivers as a source of fresh water for thousands of years.
• Water is taken directly from rivers and then treated (cleaned) before it is safe to drink.
• Rivers are one of the most common and important sources of fresh water in the world.
• However, rivers can become polluted (dirtied) by farming chemicals, factory waste, and sewage, which makes the water unsafe if it is not properly cleaned.

Example: The River Nile in Africa and the River Ganges in India are major sources of fresh water for millions of people.

2. Reservoirs

A reservoir is a large, human-made (artificial) lake that stores water.

• Reservoirs are built by constructing a dam (a large wall or barrier) across a river. This blocks the river's flow and causes water to collect behind the dam, forming the reservoir.
• The stored water can then be released and used as needed, especially during dry periods when rivers have less water.
• Reservoirs are very useful because they store large amounts of water over a long time.
• They help supply water to towns and cities, and can also be used for irrigation (watering crops on farms).

Think of it this way: A reservoir is like a giant bathtub — you fill it when water is plentiful, and use it when water becomes scarce.