CBSE Class 7 Social Science Geography NCERT Solution with summary
Chapter 5 Water
Summary of Chapter 5: Water
Water is one of the most important things on Earth. We see it in rivers, lakes, oceans, and even as rain. It keeps us alive and is essential for plants, animals, and human beings. Even though three-fourths of the Earth is covered with water, not all of it is fit for drinking.
Water Cycle
The water cycle is the process through which water moves between the Earth and the atmosphere. It has three main steps:
1. Evaporation – The Sun heats water in rivers, lakes, and oceans, turning it into vapor.
2. Condensation – The vapor cools down, forms clouds, and turns back into tiny water droplets.
3. Precipitation – When the droplets become heavy, they fall as rain, snow, or hail.
This cycle keeps repeating, ensuring that Earth never runs out of water.
Sources of Water
Freshwater is found in:
- Rivers (like the Ganga and Yamuna)
- Lakes
- Glaciers (frozen water in mountains)
- Underground water (wells and tube wells)
Most of the Earth's water (97.3%) is in oceans and seas, but this water is salty and not fit for drinking. Only 2.7% of water is fresh, and out of that, most is frozen in ice caps.
Salinity and the Dead Sea
The amount of salt in water is called salinity. Ocean water is salty because it has minerals washed away from rocks. The Dead Sea in Israel has very high salt levels (340 grams per liter), so people can easily float in it!
Ocean Circulation
Unlike lakes and ponds, ocean water is always moving. It moves in three ways:
1. Waves – When the wind blows over the ocean, it forms waves.
2. Tides – The rise and fall of ocean water due to the Moon’s and Sun’s gravity.
- Spring Tide (strong tides) occurs during the full moon and new moon.
- Neap Tide (weak tides) occurs when the Moon is at its first and last quarter.
3. Ocean Currents – Large movements of ocean water.
- Warm currents move from the equator to the poles.
- Cold currents move from the poles to the equator.
- Example: Gulf Stream (warm), Labrador Current (cold)
Ocean currents affect climate and fishing. Places where warm and cold currents meet have foggy weather and are good fishing areas.
Tsunami – The Giant Wave (December 26, 2004)
A tsunami is a huge tidal wave caused by an underwater earthquake, volcanic eruption, or landslide. On December 26, 2004, a tsunami in the Indian Ocean was caused by a 9.0 magnitude earthquake near Sumatra. It moved at a speed of 800 km per hour and hit the coasts of India, Sri Lanka, and Indonesia, killing over 10,000 people.
Before a tsunami, water suddenly pulls back from the shore. Many people didn’t know this, so they stayed at the beach and got hit by the huge waves. Early warning systems are now placed in many countries to prevent such disasters.
Water Scarcity and Conservation
Even though there is so much water on Earth, many places suffer from water scarcity because:
1. Pollution – Industrial waste and chemicals make water dirty.
2. Overuse – People waste too much water.
3. Climate Change – Less rainfall leads to water shortage.
Ways to conserve water:
- At home – Turn off taps while brushing, fix leaks, use less water while washing clothes.
- At school – Use water wisely in toilets, avoid wasting drinking water.
- At community level – Rainwater harvesting (collecting and storing rainwater).
World Water Day (March 22)
To spread awareness about saving water, March 22 is celebrated as World Water Day. People organize events to teach the importance of saving and managing water resources.
~~The END~~
Chapter 5 Water
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