Water

Overview

Water is a foundational topic in Environmental Studies for TN TET Paper I, connecting everyday life to science, health and civic responsibility. Questions typically test factual recall (sources, water cycle stages, diseases) alongside application-based reasoning (why we boil water, how forests affect rainfall). Expect 2–4 questions directly on water, with possible overlap in health/hygiene and Tamil Nadu environment sections.

To score well, you must know the water cycle with correct terminology, distinguish safe versus unsafe water sources, list common water-borne diseases with their causative agents, and understand conservation methods relevant to Indian/Tamil Nadu contexts. This topic also appears in pedagogy questions asking how to teach water concepts through activities.

Key Concepts

**Water as a universal solvent**: Water dissolves more substances than any other liquid, making it essential for life processes and also vulnerable to contamination.

**Three states of water**: Water exists as solid (ice), liquid (water) and gas (water vapour). State changes are reversible and driven by temperature.

**The water cycle is a closed system**: The same water circulates endlessly through evaporation, condensation, precipitation and collection. No new water is created on Earth.

**Safe water ≠ clear water**: Water may look clean but contain invisible pathogens or dissolved chemicals. Appearance alone does not indicate potability.

**Groundwater depletion is a major Indian concern**: Over-extraction of wells and borewells lowers the water table, causing wells to dry up and land subsidence.

**Rainwater harvesting captures water at source**: Collecting rain before it runs off reduces dependence on groundwater and prevents urban flooding.

**Water-borne diseases spread through the faecal-oral route**: Contaminated water carries pathogens from human/animal waste to new hosts, especially where sanitation is poor.

Formulas / Key Facts

| Fact | Detail | |------|--------| | Earth's water distribution | ~97% saline (oceans), ~2% frozen (glaciers), <1% available freshwater | | Main freshwater sources | Rivers, lakes, ponds, wells, borewells, springs, rainwater | | Water cycle stages | Evaporation → Condensation → Precipitation → Collection (runoff/infiltration) | | Transpiration | Water loss from plant leaves; contributes to atmospheric moisture | | Boiling kills pathogens | Boiling water for 1–3 minutes destroys most bacteria, viruses and parasites | | Chlorination | Adding chlorine (bleaching powder) disinfects water; used in municipal supply | | Filtration methods | Cloth filtering, sand filter, ceramic candle filter, RO (Reverse Osmosis) | | Tamil Nadu rainwater harvesting | Mandatory for buildings since 2003; rooftop collection and percolation pits | | WHO safe drinking water | Free from pathogens, harmful chemicals; acceptable taste, odour, appearance |

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Q1 · Water · EASY
A teacher wants to demonstrate the water cycle to Class 3 students. She heats water in a pan, and water vapour rises. She holds a cold plate above the vapour, and water droplets form on it. Which process does the formation of water droplets on the cold plate represent?
Q2 · Water · MEDIUM
In a village, people collect rainwater in tanks during the monsoon and use it throughout the year. They also dig ponds to allow rainwater to seep into the ground. What is the main purpose of letting rainwater seep into the ground?
Q3 · Water · MEDIUM
A family drinks water from a well. After heavy rains, some children in the family develop diarrhoea and stomach pain. The doctor says it is due to contaminated water. Which of the following is the most likely reason for water contamination in the well after rains?
Q4 · Water · MEDIUM
A science teacher asks students to purify muddy water collected from a pond. The students are given cotton cloth, sand, gravel, and charcoal. They set up layers of gravel, sand, and charcoal in a plastic bottle with a hole at the bottom and pour the muddy water through it. The water that comes out is clearer but may still contain germs. Which additional step should be taken to make the water safe for drinking?
Q5 · Water · HARD
A teacher explains that water in a lake decreases in summer even when there is no withdrawal of water by people. She draws a diagram showing the sun, the lake, and clouds. She wants students to understand that water is not lost but changes form and location. According to the water cycle, what happens to the water that disappears from the lake in summer?

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Notes generated on 27 Jun 2026

Water

Water

Overview

Key Concepts

Formulas / Key Facts

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