Water

14. Water

Introduction: Suppose for some reason your family gets only one bucket of water everyday for a week. Imagine what would happen! You would not be able to cook, clean vessels, wash clothes or bathe. Water is essential for life.

Where do we get water from?

We get water from rivers, springs, ponds, wells or hand pumps. Water in taps also comes from these sources.

Oceans and Seas: About two-thirds of the Earth is covered with water. Most of this water is in oceans and seas. It is saline (salty) and not fit for drinking or agriculture.

Water Cycle

The circulation of water from earth to atmosphere and back to earth.

1. Evaporation: Water from oceans, rivers, and lakes turns into vapour due to heat from the Sun. Salt is left behind.
2. Transpiration: Plants release excess water into air as water vapour through leaves.
3. Condensation: As water vapour goes higher, it cools down and turns back into tiny water droplets. These droplets float in air and form Clouds.
4. Precipitation: When clouds become too heavy, water falls down as Rain, Hail or Snow.

Back to the Oceans

Rainwater flows into rivers and streams, which eventually flow into the ocean. Some rainwater seeps into the ground and becomes Groundwater. This is the source for wells, tube wells and lakes.

Problems:

• Heavy Rains (Floods): Rise in water level of rivers. Submerge land, crops, villages. Damage to property and life.
• No Rain (Drought): Soil dries up. Water level in ponds/wells goes down. Food and fodder become scarce.

Conservation of Water

Only a small fraction of water on Earth is available for use. We must conserve it.

Rainwater Harvesting: "Catch the rain where it falls".

• Rooftop Harvesting: Collect rainwater from roof into a storage tank through pipes. Filter it before use.
• Roadside Drains: Allow water to go directly into the ground to recharge groundwater.

Chapter Summary

• Water is essential for life.
• Water cycle involves evaporation, transpiration, condensation and precipitation.
• Heavy rains may lead to floods.
• Lack of rains for long periods may lead to droughts.
• The amount of usable water on earth is limited so it needs to be used carefully.

Exercise Q1: Fill in the blanks

• The process of changing of water into its vapour is called Evaporation.
• The process of changing water vapour into water is called Condensation.
• No rainfall for a year or more may lead to Drought in that region.
• Excessive rains may cause Floods.

Exercise Q2: State whether Evaporation or Condensation

• Water drops appear on the outer surface of a glass containing cold water. (Condensation)
• Steam rising from wet clothes while they are ironed. (Evaporation)
• Fog appearing on a cold winter morning. (Condensation)
• Blackboard dries up after wiping it. (Evaporation)
• Steam rising from a hot girdle when water is sprinkled on it. (Evaporation)

Exercise Q3: True or False

• Water vapour is present in air only during the monsoon. (False)
• Water evaporates into air from oceans, rivers and lakes but not from the soil. (False)
• The process of water changing into its vapour is called evaporation. (True)
• The evaporation of water takes place only in sunlight. (False)
• Water vapour condenses to form tiny droplets of water in the upper layers of air where it is cooler. (True)

Exercise Q4

Q: Suppose you want to dry your school uniform quickly. Would spreading it near an angithi or heater help? If yes, how?

Exercise Q6

Q: Take out a cooled bottle of water from refrigerator and keep it on a table. After some time you notice a puddle of water around it. Why?

Exercise Q7

Q: To clean their spectacles, people often breathe out on glasses to make them wet. Explain why the glasses become wet.

Exercise Q8

Q: How are clouds formed?

Exercise Q9

Q: When does a drought occur?

Key Facts and Definitions