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Tamil Nadu (TNBSE)Class 4 Science★ 5-6 marks in TN Class 4 Term 2 exams — water cycle in detail, water purification stages, water pollution types

Water

Samacheer Kalvi (TN State Board) Class 4 Science — Chapter 6, Water. Water sources and conservation methods. Study notes, key concepts, worked examples, practice questions and quick revision for exam preparation.

⏱ 12 min readMedium difficulty✓ Free · NCERT-aligned

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

1Explain the water cycle with 4 stages: evaporation (water→vapour), condensation (vapour→clouds), precipitation (rain/snow), collection (rivers/lakes/groundwater)
2Describe the 3 stages of water purification: sedimentation (heavy particles settle), filtration (water passes through sand and gravel layers), chlorination (chlorine added to kill germs)
3Identify 3 types of water pollution: domestic sewage, industrial waste, agricultural runoff (fertilisers and pesticides)
4Suggest 2 ways to prevent water pollution: do not dump garbage in water bodies, treat sewage before releasing, reduce use of chemical fertilisers

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Why this chapter matters

Class 4 Water goes deeper into the water cycle with proper terminology (evaporation, condensation, precipitation, collection), the stages of water purification (sedimentation, filtration, chlorination), and types of water pollution. Tamil Nadu's dependence on monsoon rains and its history of water management — from the ancient Kallanai dam (built by Karikala Chola ~2000 years ago and still functioning!) to modern desalination plants — makes this chapter especially relevant. Children learn not just the science but the civilisational importance of water.

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Water — Class 4 Science (Samacheer Kalvi)

TN State Board (Samacheer Kalvi) Class 4 Science, Chapter 6. Water sources and conservation methods.

1. About this chapter

This chapter covers Water as part of the Class 4 Samacheer Kalvi Science curriculum. It deals with water sources and conservation methods and builds conceptual understanding essential for the TN School Term Exam.

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

List sources of fresh water
Explain methods of water conservation

2. Key concepts

Concept 1: List sources of fresh water.
Concept 2: Explain methods of water conservation.

3. Important terms and formulas

Term / Formula	Description
List sources of fresh…	List sources of fresh water
Explain methods of water…	Explain methods of water conservation

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 4 Science — Chapter 6: Water.
Core idea: Water sources and conservation methods.
Key outcomes: List sources of fresh water; Explain methods of water conservation.
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.

The water cycle — 4 stages

1. Evaporation → Sun heats water in oceans/rivers/lakes, turns to water vapour. 2. Condensation → water vapour rises, cools, forms tiny droplets that gather as clouds. 3. Precipitation → when droplets become too heavy, they fall as rain, snow, or hail. 4. Collection → water collects in rivers, lakes, ponds, and seeps underground as groundwater. The cycle repeats.

The total amount of water on Earth is constant — about 1.4 billion cubic kilometres. The same water molecules have been cycling for billions of years. The water you drink today may have been drunk by a dinosaur 100 million years ago.

Water purification stages

Sedimentation → water sits in large tanks; heavy particles (sand, mud) settle at the bottom. Filtration → water passes through layers of sand, gravel, and charcoal; smaller particles and some germs are removed. Chlorination → a small amount of chlorine is added to kill remaining bacteria and viruses. The water is now safe to drink (potable).

In Chennai, the city gets drinking water from multiple sources: reservoirs (Poondi, Red Hills, Chembarambakkam), groundwater (wells), Krishna river water (from Andhra via Telugu Ganga project), and desalination plants (Nemelli, Minjur — converting seawater to drinking water).

Water pollution

Types: Domestic sewage → untreated household waste water released into rivers. Industrial waste → factories releasing chemicals, heavy metals, and hot water. Agricultural runoff → fertilisers, pesticides, and animal waste washed from farms into water bodies. Effects: kills fish and aquatic life, makes water unfit for drinking, spreads diseases.

The Cauvery river dispute between Tamil Nadu and Karnataka is fundamentally about water access. The river is the lifeline of Tamil Nadu's agriculture. This is not just a science topic — it is the most important political and survival issue in the state.

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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 evaporation only happens from oceans

✓ Evaporation happens from ALL water bodies — rivers, lakes, ponds, puddles, wet clothes, even your skin (sweat). Plants also release water vapour through transpiration from leaves. Together, evaporation + transpiration = evapotranspiration.

WATCH OUT

✗ Thinking groundwater is a separate, unlimited source

✓ Groundwater comes from rain that seeps into the ground. If we pump out groundwater faster than rain replenishes it, the water table drops. Many parts of Tamil Nadu face severe groundwater depletion.

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