Water

Hydrosphere

• Hydrosphere = all the water found on Earth (oceans, seas, rivers, lakes, glaciers, groundwater, and water vapour).
• About 71% of Earth’s surface is water.
• 97% → salt water (oceans/seas).
• 3% → fresh water (glaciers, ice caps, rivers, lakes, groundwater).

Water Cycle

• Nitrogen (78%) – important for plants (absorbed via bacteria).
• Oxygen (21%) – essential for respiration and burning.
• Other gases (1%) – carbon dioxide, argon, ozone, etc.
• Also contains water vapour, dust particles.

Water Cycle

• Continuous circulation of water in nature.
• Evaporation – water turns to vapour.
• Condensation – vapour forms clouds.
• Precipitation – rain, snow, hail.
• Collection – rivers, oceans, lakes store water.

Movements of Ocean Water

1. Waves
• Rise & fall of water on ocean surface, mainly caused by wind.
• High waves = tsunami (due to undersea earthquake/volcano).
2. Tides
• Regular rise & fall of sea level.
• Caused by gravitational pull of Moon & Sun.
• High tide → water level rises.
• Low tide → water level falls.
• Used for fishing, navigation, electricity generation.
3. Ocean Currents
• Streams of ocean water flowing constantly in a specific direction.
• Warm currents (from equator → poles).
• Cold currents (from poles → equator).
• Influence climate of coastal regions.

Importance of Water

• Essential for life (drinking, agriculture, industries).
• Maintains Earth’s climate.
• Source of transport, energy, and food (fishing).

Problems & Conservation

• Water scarcity due to overuse, pollution, uneven distribution.
• Need to conserve water → rainwater harvesting, reducing wastage, afforestation.