Water as a Resource Chapter Notes | Science Class 3 ICSE PDF Download

Introduction

Change of State of Water

• Water changes its form due to temperature changes.
• Melting occurs when ice is heated and turns into liquid water.
• Evaporation happens when water is heated slowly, turning into water vapor.
• Boiling is when water is heated quickly, changing into water vapor.
• Condensation occurs when water vapor cools and turns back into liquid water.
• Freezing or solidification happens when water is cooled and turns into ice.

Water Cycle

• The water cycle is the continuous movement of water between the Earth and the sky.
• The sun heats water in rivers, seas, lakes, and oceans, causing evaporation into water vapor.
• Water vapor rises, cools, and condenses into tiny water droplets, forming clouds.
• Heavy clouds release water as precipitation, such as rain, snow, sleet, or hail.
• Rainwater and melted snow flow back into water bodies or soak into the ground, restarting the cycle.
• Water helps control the Earth’s temperature.

Water and Impurities

• Pure water has no color, taste, or smell but can dissolve many substances.
• During evaporation, water vapor dissolves gases in the air.
• Rainwater mixes with dust, germs, and other substances, making it impure.
• Water on Earth is not pure and contains impurities like mud, dirt, sand, and germs, making it unsafe for direct use.

Types of Impurities

• Soluble impurities: Gases, salts, minerals, and chemicals that dissolve in water and change its properties.
• Insoluble impurities: Mud, dust, sand, clay, oil, and plant or animal material that do not dissolve in water.

Causes of Water Impurities

• Uncovered water collects germs, dirt, and dust.
• Industrial waste and sewage pollute water bodies.
• Human activities like washing, cleaning, and bathing in water bodies make water unfit for use.

Purification of Water

• Impurities in water make it unsafe and can cause diseases like cholera, typhoid, and dysentery.
• Water purification removes harmful substances to make water safe for drinking.

Methods of Water Purification

• Filtration: Removes insoluble impurities using filter paper or fine muslin cloth, leaving clean water.
• Boiling: Kills germs by boiling water for 10-15 minutes and storing it in clean, covered containers.
• Chlorination: Uses chlorine tablets to kill germs and prevent waterborne diseases.

Rainwater Harvesting

• Water scarcity is a major issue, so conserving water is important.
• Rainwater harvesting is a simple, cost-effective method to collect and store rainwater for future use.
• It reduces the need for tap water and lowers water bills.

Methods of Rainwater Harvesting

• Rooftop harvesting: Collects rainwater from rooftops and stores it in tanks for uses like flushing toilets, laundry, mopping, washing, and gardening.
• Collecting rainwater in containers like buckets, drums, or tubs for later use.
• Digging wells and borewells to increase groundwater levels.

Terms to Know

• Melting: When a solid turns into a liquid due to increased temperature.
• Evaporation: When a liquid turns into a gas due to heating.
• Condensation: When a gas turns into a liquid due to cooling.
• Freezing: When a liquid turns into a solid due to cooling.
• Water cycle: The continuous movement of water between the sky and Earth.
• Impurities: Substances that make water dirty or unsafe.
• Soluble impurities: Substances that dissolve in water.
• Insoluble impurities: Substances that do not dissolve in water.
• Water purification: The process of removing harmful substances to make water safe for drinking.
• Filtration: Removing insoluble impurities by passing water through a filter.
• Boiling: Heating water to kill germs.
• Chlorination: Using chlorine to purify water.
• Rainwater harvesting: Collecting and storing rainwater for future use.