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Tamil Nadu (TNBSE)Class 3 Science★ 5-6 marks in TN Class 3 Term 2 exams — sources of water, potable water, conservation methods, and short written answers

Water

Samacheer Kalvi (TN State Board) Class 3 Science — Chapter 6, Water. The water cycle and rainwater harvesting. Study notes, key concepts, worked examples, practice questions and quick revision for exam preparation.

⏱ 10 min readEasy difficulty✓ Free · NCERT-aligned

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By the end of this chapter you'll be able to…

1State that rain is the main source of all freshwater on Earth
2Recall that only 3% of Earth's water is freshwater
3Define potable water as water that is safe for drinking
4Name at least 4 sources of water: rain, well, river, lake, sea
5Explain that boiling is the simplest method to kill germs in water and make it potable
6Identify the sea as the largest water source on Earth (salt water, not drinkable)
7List 3 ways to save water at home: do not let buckets overflow, wash fruits/vegetables in a bowl instead of running water, turn off taps while brushing and after use
8Suggest 2 ways to conserve water bodies: deepen ponds and lakes, plant trees on banks, reduce pollution in rivers and lakes

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Why this chapter matters

Only 3% of Earth's water is freshwater — and most of that is locked in glaciers. This chapter teaches Class 3 children that water is precious and finite. They learn that rain is the primary source of all freshwater, how to make water safe for drinking (boiling kills germs — potable water), different water bodies (sea, lake, river, well), and most critically, how to conserve water at home and in the community. Tamil Nadu has faced severe water crises — this chapter is not just science, it is survival education for a TN child.

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Water — Class 3 Science (Samacheer Kalvi)

TN State Board (Samacheer Kalvi) Class 3 Science, Chapter 6. The water cycle and rainwater harvesting.

1. About this chapter

This chapter covers Water as part of the Class 3 Samacheer Kalvi Science curriculum. It deals with the water cycle and rainwater harvesting and builds conceptual understanding essential for the TN School Term Exam.

By the end of this chapter, students will be able to:

Describe the water cycle
Explain the need for rainwater harvesting

2. Key concepts

Concept 1: Describe the water cycle.
Concept 2: Explain the need for rainwater harvesting.

3. Important terms and formulas

Term / Formula	Description
Describe the water cycle…	Describe the water cycle
Explain the need for…	Explain the need for rainwater harvesting

4. Worked examples

Example 1. Applying a key concept from this chapter.

Solution: Identify the relevant principle → apply the formula or rule → state the answer with correct units.

Example 2. A typical exam-style question on water.

Solution: Break the problem into steps, use the appropriate formula and verify the answer.

5. Common mistakes

Mistake: Skipping units or forgetting to state them. Fix: Always write units alongside every quantity and answer.
Mistake: Confusing similar terms or concepts in this chapter. Fix: Make a comparison table of the terms during revision.

6. Practice (exam-style)

Define the main term or principle covered in Chapter 6.
Give two real-life examples related to water.
Solve a short numerical or descriptive question from this chapter.
State one important formula and explain each symbol.

7. Answer key (hints)

Refer to section 2 (Key concepts) above for the definition.
Examples should be drawn from daily experience and local context.
Apply the formula from section 3, show all steps clearly.
Formula with units — refer to the textbook glossary for symbol meanings.

8. Quick revision

Class 3 Science — Chapter 6: Water.
Core idea: The water cycle and rainwater harvesting.
Key outcomes: Describe the water cycle; Explain the need for rainwater harvesting.
Always revise diagrams / tables from the Samacheer Kalvi textbook before the exam.

Key formulas & results

Everything you need to memorise, in one card. Screenshot this for revision.

Sources of water

Rain → primary source of all freshwater. Well → water from underground (groundwater). River → flowing freshwater. Lake → still freshwater body in low-lying areas. Pond → small still water body. Sea → largest water body on Earth, salt water, not drinkable.

When it rains, the water follows a path: it seeps into the ground, is absorbed by plants, and flows into rivers/lakes/oceans. This is part of the water cycle.

Potable water

Potable water = water that is safe to drink. It is clean, free of germs and harmful chemicals. Methods to make water potable: boiling (simplest — kills all germs), filtering (removes dirt), chlorination (adding small amounts of chlorine in water treatment plants), RO/UV purifiers (modern methods).

Just because water looks clean does not mean it is potable. Invisible germs can cause diseases. Always boil water from wells, ponds, or unknown sources before drinking.

Saving water at home

1. Do not let buckets overflow — turn off the tap when the bucket is full. 2. Wash fruits and vegetables in a bowl of water, not under a running tap. 3. Turn off the tap while brushing teeth and after every use. 4. Fix leaking taps immediately — a dripping tap wastes thousands of litres a year. 5. Use water used for washing rice/vegetables to water plants.

Every drop counts. Chennai's 2019 'Day Zero' water crisis showed what happens when water is not conserved. The city nearly ran out of water.

Conserving water bodies

Deepen ponds and lakes → increases water storage capacity. Plant trees on the banks of rivers and lakes → tree roots hold soil and prevent silting. Reduce pollution → do not dump garbage, plastics, or factory waste in water bodies. Rainwater harvesting → collect and store rainwater from rooftops for later use.

Tamil Nadu was the first state in India to make rainwater harvesting mandatory for all buildings (since 2003). This is a point of pride and a practical lesson for every TN student.

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Common mistakes & fixes

These are the exact errors that cost students marks in board exams. Read them once, save yourself the trouble.

WATCH OUT

✗ Thinking sea water can be made potable by just boiling

✓ Boiling kills germs but does NOT remove salt. Sea water has dissolved salt that boiling cannot remove. To make seawater drinkable, you need desalination (removing salt), which is a very expensive industrial process. Only 3% of Earth's water is freshwater — the 97% in seas and oceans is saline.

WATCH OUT

✗ Washing vehicles with a running hose instead of a bucket

✓ A running hose can waste 100-200 litres in a single vehicle wash. A bucket uses only 15-20 litres. Always use a bucket and a wet cloth to wash vehicles.

WATCH OUT

✗ Throwing garbage, especially plastic, into rivers and lakes

✓ Plastic takes hundreds of years to degrade. It pollutes water, kills fish and aquatic life, and clogs waterways. Always dispose of garbage in dustbins, never in water bodies.

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