Water — Class 6 Physical Science
'Water is life — from the Krishna river to a raindrop, every drop counts.'
1. Introduction
Water is essential for all living things. We drink it, use it for cooking, cleaning, farming, and industry. Yet, only a tiny fraction of Earth's water is usable freshwater.
Why This Chapter Matters
- Understand the water cycle — nature's recycling system
- Learn about water conservation (critical in AP)
- Understand floods and droughts
- Foundation for environmental science
2. Sources of Water
Natural Sources
| Source | Description | Example in AP |
|---|---|---|
| Oceans | Salt water (97% of Earth's water) | Bay of Bengal (AP coast) |
| Rivers | Fresh water flowing to sea | Krishna, Godavari, Penna |
| Lakes | Fresh water in depressions | Kolleru Lake |
| Ponds | Small bodies of still water | Village ponds |
| Groundwater | Water under the ground | Wells, borewells |
| Rain | Water from clouds | Monsoon rains |
| Glaciers | Frozen fresh water | Himalayas (not in AP) |
Types of Water
| Type | Salt Content | Where Found | Can We Drink? |
|---|---|---|---|
| Freshwater | Very low | Rivers, lakes, rain, glaciers | YES |
| Brackish water | Medium | Estuaries (where river meets sea) | No (but some animals live here) |
| Saline water | High | Oceans, seas | No |
Water Availability
- 97% of Earth's water is in oceans (salt water)
- 2% is frozen in glaciers and ice caps
- Only 1% is usable freshwater
- 'Less than 1% of all water on Earth is available for us to drink'
3. The Water Cycle
The water cycle is the continuous movement of water between the earth and the atmosphere.
Stages of the Water Cycle
Clouds (Condensation)
↗ ↖
/ \
/ \
↑ ↓ Precipitation (Rain)
↑ Evaporation
Water bodies (Oceans, rivers, lakes)
Stage 1: Evaporation
- Sun heats water in oceans, rivers, lakes, ponds
- Water turns into water vapour (gas)
- Rises into the atmosphere
- 'Even the moisture from your wet clothes after a bath evaporates into the air'
Stage 2: Transpiration
- Plants release water vapour through their leaves
- Also called evapotranspiration
- A large tree can release hundreds of litres of water per day
Stage 3: Condensation
- Water vapour rises and cools
- Changes back from gas to tiny water droplets
- These droplets form clouds
- 'When you see your breath on a cold day, you are seeing condensation'
Stage 4: Precipitation
- When water droplets in clouds become too heavy
- They fall as rain, snow, hail, or sleet
- In AP: most rainfall comes from the southwest monsoon (June-September)
The Cycle Continues
Water returns to oceans, rivers, and soil → evaporation starts again
Importance of the Water Cycle
- Distributes water around the world
- Replenishes freshwater sources
- Regulates climate
- Supports all life
4. Water Conservation
Why Conserve Water?
- Only 1% of Earth's water is usable
- Population is growing → demand increases
- Climate change → more droughts and floods
- AP: Rayalaseema region faces water scarcity
Ways to Conserve Water
At Home
| Method | Water Saved |
|---|---|
| Turn off tap while brushing | ~10 litres per minute |
| Fix leaking taps | ~100 litres per day |
| Use mug, not running tap, for bathing | ~50 litres per bath |
| Collect rainwater for gardening | Varies |
| Wash vegetables in a bowl, not running tap | ~20 litres |
In Farming
- Drip irrigation: water goes directly to plant roots (AP farmers use this)
- Sprinkler irrigation: waters like rain
- Mulching: covering soil to reduce evaporation
- Growing less water-intensive crops
5. Rainwater Harvesting
Collecting and storing rainwater for later use.
Methods
Rooftop Harvesting
- Rain falls on roof
- Water flows through pipes (via filter)
- Stored in tanks or recharged into ground
Pit / Pond Harvesting
- Digging pits/ponds to allow rainwater to seep into the ground
- Recharges groundwater
Benefits
- Replenishes groundwater
- Reduces water bills
- Prevents flooding
- Provides water in dry seasons
AP Context
- Andhra Pradesh has made rainwater harvesting mandatory for new buildings in some cities
- Mission Kakatiya in Telangana (similar: AP's tank restoration) — restoring ancient water tanks
- Many villages in AP have traditional water harvesting structures (kuntas, cheruvus)
6. Floods and Droughts
Floods
When there is too much rain, rivers overflow their banks.
Causes:
- Heavy rainfall (especially during monsoon)
- Deforestation (trees absorb less water)
- Poor drainage systems
- Cyclones (AP coast is cyclone-prone)
Effects:
- Damage to homes, crops, roads
- Loss of life and property
- Water-borne diseases
- In AP: coastal districts (Krishna, Godavari, Visakhapatnam) are flood-prone
Droughts
When there is too little rain over a long period.
Causes:
- Low rainfall
- Climate change
- Overuse of groundwater
- Deforestation
Effects:
- Crop failure
- Drinking water shortage
- Famine
- In AP: Rayalaseema region (Anantapur, Kurnool, Chittoor, Kadapa) frequently faces drought
AP Context: Krishna-Godavari Water
The Krishna and Godavari rivers are the lifelines of Andhra Pradesh.
| River | Length | Significance |
|---|---|---|
| Godavari | ~1465 km | Largest river in peninsular India; major irrigation source |
| Krishna | ~1400 km | Second largest; waters Guntur, Krishna districts |
| Penna | ~597 km | Seasonal river; flows through Rayalaseema |
Water Sharing:
- Water from these rivers is shared between AP, Telangana, Karnataka, and Maharashtra
- Disputes over water allocation affect farming
Rayalaseema Drought
- Rayalaseema (Anantapur, Kurnool, Kadapa, Chittoor) receives very low rainfall (~500-700 mm/year)
- Frequent drought conditions
- Farmers rely on groundwater (overused, depleting)
- Solutions: rainwater harvesting, drip irrigation, drought-resistant crops (millets)
7. Common Mistakes — Fix Them Now
| # | Mistake | Correction |
|---|---|---|
| 1 | Thinking the same water we drink is new water | Water on Earth is recycled through the water cycle — the water we drink may have been dinosaur water! |
| 2 | Believing evaporation only happens from oceans | Evaporation happens from ALL water bodies — rivers, lakes, ponds, even from your wet clothes |
| 3 | Confusing condensation and evaporation | Evaporation: liquid → gas (goes up). Condensation: gas → liquid (comes down). |
| 4 | Thinking floods and droughts can't happen in the same region | Rayalaseema has droughts; coastal AP has floods. Some regions can have both in different years. |
| 5 | Calling all rain 'fresh' | Rain is generally fresh, but can become acidic in polluted areas (acid rain). |
8. Exam Focus
Marks Blueprint
| Question Type | Marks | Topic |
|---|---|---|
| MCQ | 1 | Water cycle / source |
| Short answer | 2 | Evaporation / condensation |
| Short answer | 2 | Rainwater harvesting |
| Long answer | 3 | Water cycle / conservation |
| AP context | 3 | Krishna-Godavari / Rayalaseema drought |
Quick Self-Test (5 Questions)
Q1: What percentage of Earth's water is freshwater available for drinking?
<details><summary>Answer</summary>Less than 1%.</details>Q2: What is the process by which water changes from liquid to gas?
<details><summary>Answer</summary>Evaporation.</details>Q3: Name two methods of rainwater harvesting.
<details><summary>Answer</summary>Rooftop harvesting (collecting from roof) and pit/pond harvesting (recharging groundwater).</details>Q4: Which rivers are the main water sources for Andhra Pradesh?
<details><summary>Answer</summary>Godavari and Krishna rivers.</details>Q5: Why does Rayalaseema frequently face drought?
<details><summary>Answer</summary>Low rainfall (~500-700 mm/year), overuse of groundwater, and seasonal rivers that depend on monsoon.</details>9. Chapter Summary
- Sources: oceans (97%), glaciers (2%), freshwater (1%) — rivers, lakes, groundwater, rain
- Water cycle: Evaporation → Condensation → Precipitation → Collection → (repeat)
- Conservation: fix leaks, turn off taps, drip irrigation, rainwater harvesting
- Rainwater harvesting: rooftop collection, groundwater recharge
- Floods: excess rain (coastal AP); Droughts: water scarcity (Rayalaseema)
- AP context: Krishna-Godavari rivers, Rayalaseema drought, traditional water tanks
'Water is precious — every drop conserved today is a drop available tomorrow. Save water, save life.'
