Class 6 Science Notes Chapter 14 (Water) – Science Book

Detailed Notes with MCQs of Chapter 14, 'Water'. This is an extremely important topic, not just for your exams but for understanding life itself. Water is fundamental. Pay close attention as we break down the key concepts for your government exam preparation.

Chapter 14: Water - Detailed Notes

1. Importance and Uses of Water:

• Essential for Life: All living organisms (plants, animals, humans) need water to survive.
• Daily Activities: Used for drinking, bathing, cooking, washing clothes, cleaning, flushing toilets.
• Agriculture: Crucial for growing crops (irrigation). A large amount of water is used for agriculture.
• Industries: Used in various manufacturing processes, as a coolant, and for generating electricity (hydroelectric power).
• Transportation: Rivers, lakes, and oceans are used for transporting goods and people.

2. Sources of Water:

• Surface Water: Water present on the surface of the Earth.
  • Rain: The primary source of freshwater.
  • Rivers: Flowing bodies of water, often originating from mountains (melting snow/glaciers) or springs, fed by rain.
  • Lakes: Large bodies of standing water, fed by rivers and rain.
  • Ponds: Smaller bodies of standing water.
  • Oceans and Seas: Contain saltwater, making up the vast majority of Earth's water. Not directly usable for drinking or most agriculture without desalination.
• Groundwater: Water found beneath the Earth's surface in the soil pore spaces and fractures of rock formations.
  • Wells, Tube Wells, Hand Pumps: Used to draw groundwater.
  • Springs: Places where groundwater naturally flows out onto the surface.
  • Water Table: The upper level of the underground surface below which the ground is saturated with water. The depth of the water table varies with location and season.
  • Infiltration/Seepage: The process by which rainwater soaks into the ground, recharging groundwater.

3. The Water Cycle:

• The continuous circulation of water on, above, and below the surface of the Earth. It ensures water availability.
• Key Processes:
  • Evaporation: The process where liquid water changes into water vapour (a gas) due to heat, primarily from the sun. Water from oceans, rivers, lakes evaporates.
  • Transpiration: The process where plants release water vapour into the atmosphere through tiny pores (stomata) in their leaves. This is a significant contributor to atmospheric moisture.
  • Condensation: The process where water vapour in the air cools down and changes back into tiny liquid water droplets or ice crystals, forming clouds. This happens at higher altitudes where it's colder.
  • Precipitation: Water falling back to Earth from clouds in the form of rain, snow, sleet, or hail.
  • Collection: Water from precipitation collects in rivers, lakes, oceans, or seeps into the ground (infiltration), restarting the cycle.

4. Impact of Rainfall Variations:

• Floods: Occur when there is excessive rainfall over a short period, causing rivers, lakes, and other water bodies to overflow their banks.
  • Consequences: Damage to property, crops, loss of human and animal life, spread of waterborne diseases.
• Droughts: Occur when there is a prolonged period with little or no rainfall.
  • Consequences: Scarcity of drinking water, crop failure, difficulty in getting fodder for animals, soil becomes dry and hard, water table level drops significantly, affects industries.

5. Water Conservation:

• The practice of using water efficiently to reduce unnecessary water usage. Crucial because freshwater is a limited resource.
• Methods:
  • Turn off taps while brushing or soaping.
  • Repair leaking taps and pipes immediately.
  • Use water judiciously for washing vehicles and watering plants (e.g., use a bucket instead of a hose, water plants in the morning/evening to reduce evaporation).
  • Reuse water where possible (e.g., water used for washing vegetables can be used for watering plants).
• Rainwater Harvesting: A key technique for conserving water and recharging groundwater.
  • Definition: Collecting rainwater from rooftops and other surfaces and storing it for later use or allowing it to seep into the ground.
  • Methods:
    • Rooftop Rainwater Harvesting: Collecting rainwater from roofs into storage tanks or directing it into pits/trenches to recharge groundwater.
    • Collecting runoff in ponds or check dams.
  • Benefits: Increases water availability, raises the water table, reduces soil erosion and flooding.

Key Terms to Remember:

• Evaporation: Liquid to Gas (Water Vapour) due to heat.
• Transpiration: Water vapour release from plants.
• Condensation: Gas (Water Vapour) to Liquid (Water Droplets/Ice Crystals) due to cooling, forming clouds.
• Precipitation: Water falling from clouds (rain, snow, etc.).
• Groundwater: Water held underground.
• Water Table: Upper level of groundwater saturation.
• Infiltration: Water soaking into the ground.
• Flood: Overflow of water due to excessive rain.
• Drought: Prolonged period of no/low rainfall.
• Rainwater Harvesting: Collecting and storing rainwater.

Multiple Choice Questions (MCQs):

1. Which of the following processes involves the conversion of liquid water into water vapour by heat?
   (a) Condensation
   (b) Precipitation
   (c) Evaporation
   (d) Infiltration

2. Plants release water vapour into the atmosphere through a process called:
   (a) Photosynthesis
   (b) Respiration
   (c) Condensation
   (d) Transpiration

3. The formation of clouds is primarily due to which process?
   (a) Evaporation
   (b) Condensation
   (c) Precipitation
   (d) Transpiration

4. What is the main source of water for rivers, lakes, and groundwater?
   (a) Oceans
   (b) Clouds
   (c) Rain
   (d) Plants

5. The upper level of groundwater beneath the Earth's surface is known as the:
   (a) Water Cycle
   (b) Water Table
   (c) Aquifer
   (d) Water Body

6. Excessive rainfall leading to the overflow of rivers and lakes causes:
   (a) Drought
   (b) Famine
   (c) Flood
   (d) Water Scarcity

7. A long period with little or no rainfall leads to a condition called:
   (a) Flood
   (b) Monsoon
   (c) Drought
   (d) Waterlogging

8. Collecting rainwater from rooftops and storing it or letting it seep into the ground is called:
   (a) Water Purification
   (b) Desalination
   (c) Rainwater Harvesting
   (d) Drip Irrigation

9. Which of the following is NOT a primary use of water in agriculture?
   (a) Irrigation of crops
   (b) Drinking water for farm animals
   (c) Generating electricity on the farm
   (d) Mixing pesticides and fertilizers

10. Which process helps in replenishing groundwater?
    (a) Evaporation
    (b) Transpiration
    (c) Condensation
    (d) Infiltration

Answer Key for MCQs:

1. (c) Evaporation
2. (d) Transpiration
3. (b) Condensation
4. (c) Rain
5. (b) Water Table
6. (c) Flood
7. (c) Drought
8. (c) Rainwater Harvesting
9. (c) Generating electricity on the farm (While water is used for hydroelectricity, it's not a primary agricultural use on a typical farm itself)
10. (d) Infiltration

Study these notes carefully. Understanding the water cycle and the importance of conservation is key. Let me know if any part needs further clarification.