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Tamil Nadu (TNBSE)Class 5 Science★ 5-6 marks in TN Class 5 Term 2 exams — choose correct answer, fill blanks, match following, short answers

Water

Samacheer Kalvi (TN State Board) Class 5 Science — Chapter 6, Water. Water cycle and water-borne disease prevention. 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…

1State that 97% of Earth's water is found in oceans and seas (saline, not directly drinkable)
2State that underground water is free from suspended impurities (naturally filtered by soil and rock layers)
3Define desalination as the artificial process of converting seawater into fresh water by removing salt
4Explain the water cycle: continuous circulation of water from Earth's surface to the atmosphere and back — evaporation, condensation, precipitation, collection
5Name the three states of water: solid (ice), liquid (water), gas (water vapour/steam)
6Identify microorganisms as the cause of waterborne diseases
7Explain rainwater harvesting: collecting and storing rainwater from rooftops to increase groundwater level; in ancient times, people used tanks (eris/ஏரி) and ooranis (ஊருணி) to store rainwater
8State that rain is the main source of fresh water

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Why this chapter matters

Water in Class 5 is a comprehensive chapter that ties together the water cycle, water resources, water purification, and water conservation. Children learn key facts: 97% of Earth's water is saline ocean water, underground water is naturally filtered and free from suspended impurities, and desalination is an artificial process to convert seawater to fresh water (critical for coastal cities like Chennai). They study rainwater harvesting not just as a concept but as a practical solution — Tamil Nadu was the first state to mandate it. They also learn that ancient Tamil civilisation used eris (tanks) and ooranis to store rainwater, connecting modern science to cultural heritage.

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Water — Class 5 Science (Samacheer Kalvi)

TN State Board (Samacheer Kalvi) Class 5 Science, Chapter 6. Water cycle and water-borne disease prevention.

1. About this chapter

This chapter covers Water as part of the Class 5 Samacheer Kalvi Science curriculum. It deals with water cycle and water-borne disease prevention 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 in detail
Explain prevention of water-borne diseases

2. Key concepts

Concept 1: Describe the water cycle in detail.
Concept 2: Explain prevention of water-borne diseases.

3. Important terms and formulas

Term / Formula	Description
Describe the water cycle…	Describe the water cycle in detail
Explain prevention of water-borne…	Explain prevention of water-borne diseases

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 5 Science — Chapter 6: Water.
Core idea: Water cycle and water-borne disease prevention.
Key outcomes: Describe the water cycle in detail; Explain prevention of water-borne diseases.
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.

Earth's water distribution

Total water on Earth: ~97% is in oceans and seas (SALINE — too salty to drink). Only ~3% is FRESHWATER. Of this 3%: ~2% is frozen in glaciers and ice caps, ~0.6% is groundwater, ~0.01% is in rivers, lakes, and ponds. Less than 1% of all Earth's water is easily accessible freshwater for human use.

This is why water conservation matters so much. The total amount of water on Earth is fixed — about 1.4 billion cubic kilometres. It has been cycling for billions of years.

Underground water and Desalination

Underground water (groundwater) → water that seeps into the ground, stored in aquifers (porous rock layers). It is naturally filtered by passing through soil, sand, and rock — so it is free from suspended impurities. However, it may contain dissolved minerals and needs testing. Desalination → artificial process of removing salt from seawater to produce fresh drinking water. Methods: Reverse Osmosis (RO) — forcing seawater through a membrane that blocks salt; Thermal desalination — boiling seawater and condensing the steam.

Chennai has two major desalination plants: Minjur (100 million litres/day) and Nemelli (100 million litres/day). These provide critical water supply to the city, especially during drought years.

Rainwater Harvesting (RWH)

Rainwater is collected from rooftops (catchment) → flows through gutters and pipes → filtered (sand, gravel, charcoal) → stored in tanks or allowed to seep into the ground through recharge pits. Benefits: increases groundwater level, reduces flooding, provides free soft water, reduces dependence on water tankers.

Ancient Tamil Nadu had a sophisticated water management system: eris (tanks/ lakes), ooranis (village ponds), kalingus (sluice gates), and check dams across rivers. The Grand Anicut (Kallanai) built by Karikala Chola ~2000 years ago on the Cauvery is still in use — one of the oldest functioning water diversion structures in the world.

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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 underground water is always 100% safe to drink without testing

✓ Underground water is free from SUSPENDED impurities (mud, sand) due to natural filtration. But it may contain DISSOLVED impurities — arsenic, fluoride, nitrates from fertilisers, or salt (especially near coastal areas). Always test borewell water before drinking.

WATCH OUT

✗ Thinking desalination is cheap and can solve all water problems

✓ Desalination is ENERGY-INTENSIVE and EXPENSIVE. It costs about ₹40-60 per 1000 litres, compared to ₹5-10 for surface water treatment. It also produces highly concentrated brine as waste, which if dumped back into the sea can harm marine life. Conservation is always cheaper and better.

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