Chapter: 09. Water As A Resource
Water as a Resource
Water is a vital resource for all life on Earth. We cannot survive without it. Water is used for many important purposes daily, including drinking, cleaning, washing, and cooking.
Here are some key properties of water:
Water is a liquid at room temperature. Water can exist in three different forms: solid (ice), liquid (water), and gas (water vapour). Water is known as a universal solvent because it can dissolve many substances.
Everyday Uses of Water
Water is essential for numerous tasks. For example:
Washing and cleaning spills, as shown by a man wiping a floor with a cloth.
Bathing and personal hygiene, like an elephant spraying water on itself.
Cooking, such as a woman pouring water into a cooking pot.
Brushing teeth, as depicted by a girl at a sink.
These examples highlight how water is fundamental to our daily lives.
Change in Forms of Water
Water can change its form when it is heated or cooled. Water exists in three forms:
One form of water can transform into another. For instance, solid water (ice) changes into liquid water when heated, and liquid water changes into solid water (ice) when cooled.
Evaporation
Evaporation is the process where a liquid changes into vapour (gas) when heated. The rate of evaporation increases significantly when the liquid is boiled.
Example: When water is boiled on a gas stove, it turns into water vapour and rises into the air. This change from liquid to gas is evaporation.
Condensation
Condensation is the opposite process of evaporation; it’s when a gas changes into a liquid upon cooling.
Example 1: When a chilled bottle is left on a table, small water droplets form on its outer surface. This happens because the water vapour present in the air cools down when it touches the cold surface of the bottle, condensing into liquid water droplets.
Example 2: If you breathe onto a cold mirror or window glass, you’ll observe tiny water droplets forming, making the surface foggy. Your breath contains unseen water vapour. When this warm vapour meets the cold glass, it cools down and condenses into visible liquid water droplets.
This demonstrates that water vapour condenses when it cools.
Water Cycle
The Earth has a fixed amount of water that continuously changes its form and moves around. The water cycle describes the journey water takes as it circulates from the land to the sky and then back to the land.
Here are the key processes in the water cycle:
Water in bodies like lakes, rivers, ponds, and oceans gets heated by the Sun’s warmth. This heat causes the liquid water to turn into water vapour (gas) and rise into the air. This is the process of evaporation. As the water vapour rises higher in the sky, it cools down. When it cools, the water vapour turns into tiny water droplets. These tiny droplets combine together to form clouds. This process is called condensation. Dew Formation: Dew forms as tiny water droplets on exposed surfaces (like leaves) in the mornings or evenings. This happens due to condensation of water vapour.
When clouds become very heavy with a large amount of water droplets, they can no longer hold the water. The water droplets then fall back to Earth in the form of rain or snow. This is known as precipitation. The water that falls as rain or snow collects in various water bodies such as lakes, rivers, and oceans, or it seeps into the ground to become groundwater. From these collection points, the water then evaporates again, rising back into the sky, and the entire cycle continues. The continuous circulation of water through the processes of evaporation, condensation, and precipitation is known as the water cycle.
Image: The water cycle showing evaporation, condensation, and precipitation.
Making Water Fit for Use
It is crucial to drink only clean water. Water from sources like wells, rivers, taps, and even underground can contain impurities, making it unsafe for direct consumption.
Impurities in water can be categorized as follows:
Insoluble impurities: These are impurities that do not dissolve in water and can be easily seen. Examples include sand, mud, tiny stones, and twigs. Activity Insight: An experiment showed that when sand, mud, stones, or twigs are mixed with water and then strained, they remain in the strainer, confirming they do not dissolve.
Soluble impurities: These impurities dissolve in water and cannot be easily seen. Examples include salt and dissolved substances in soft drinks. Activity Insight: The same experiment showed that soft drink and salt, when mixed with water and strained, pass through the strainer, indicating they are dissolved in the water. Germs: These are very tiny, harmful living organisms that cannot be seen with the naked eye. They can cause various diseases if present in drinking water. INFOHUB
It’s important to remember that about 71% of the Earth’s surface is covered with water, and the primary source of this water is rainwater.
How to Purify Water
Seawater is salty and not suitable for drinking. While water from lakes, rivers, and wells can be used, it’s generally not clean enough for direct consumption due to dirt and germs. Drinking impure water can lead to illness.
Water needs to be purified to remove germs and other impurities to make it safe for drinking.
Waterworks: Large facilities called waterworks purify water before it is supplied to homes through taps. Boiling: For places where tap water is not available or its quality is uncertain, boiling is the easiest and most effective method to purify water at home. Water should be boiled for at least 10 minutes to kill germs. Potable water is water that is safe for drinking. Waterborne diseases like cholera, typhoid, and dysentery can be caused by germs in impure water. Reflection Point: Boiling purifies water by killing harmful germs. Filtering: Even tap water, despite being purified at waterworks, can become dirty or impure during its journey to our homes. Therefore, using a water filter at home helps remove remaining dirt and impurities, ensuring cleaner drinking water.
Image: A home water filter. Chlorination: Chlorine tablets can be added to water to purify it. This process, called chlorination, kills germs that cause waterborne diseases like jaundice and cholera.
Rainwater Harvesting
Water is a source of life, and it is very important to conserve it. Rainwater harvesting is a method of collecting and storing rainwater for future use. This practice is becoming increasingly popular in many parts of India.
Collection Method: Rainwater is collected from hard surfaces, such as rooftops, to prevent it from running off and being wasted. Collection can be done from rooftops, the ground, or a combination of both.
Image: An example of rainwater harvesting, collecting water from a roof into a barrel. Uses: The collected rainwater can be used for various purposes, especially for drinking during times of water scarcity or drought. Structures for Harvesting: Rainwater harvesting can also involve building tanks and check dams to store water. The concept of rainwater harvesting emphasizes saving every drop:
“Oh water! You are a gift.
When water is scarce and rare,
Do not waste it, you dare!
You can collect water when it rains,
Use it safely, do not drain.
You may even collect it on the rooftop,
As it rains, drop by drop!
Rainwater harvesting can end our sorrows,
For a happy and nice tomorrow.”
This poem highlights the importance and benefits of collecting and saving rainwater.
Key Terms
Understanding these terms is essential for comprehending the chapter on water as a resource:
Precipitation: The falling of any form of water (like rain or snow) from the atmosphere onto the Earth’s surface. Water cycle: The continuous process by which water circulates through the Earth’s atmosphere and land, involving evaporation, condensation, and precipitation. Germs: Extremely tiny, harmful living organisms that are invisible to the naked eye but can cause diseases. Waterworks: A facility or system where water is purified and made safe for drinking before being supplied to homes and communities. Chlorination: The process of purifying drinking water by adding chlorine tablets, which effectively kill harmful germs. Rainwater harvesting: The practice of collecting and storing rainwater for later use, often to supplement water supply or for conservation.
Overall Summary: Water as a Resource
This chapter explains the importance of water, its different forms, how it moves through the environment, and how we can make it safe to use and conserve it.
Water’s Importance and Properties: Water is essential for life and daily activities. It exists as solid, liquid, and gas, and is a universal solvent. Evaporation: Liquid water turns into gas (vapour) when heated. Condensation: Gas (vapour) turns into liquid water when cooled. The Water Cycle: Water continuously circulates on Earth through: Evaporation: Water rises as vapour. Condensation: Vapour forms clouds. Precipitation: Water falls back as rain or snow. Collection: Water gathers in bodies of water or underground. Water Purification: Water from natural sources often contains impurities (insoluble, soluble, germs) and must be purified before drinking. Methods include boiling (easiest for killing germs), filtering (to remove dirt), and chlorination (using chlorine tablets to kill germs). Waterworks purify water for communities. Rainwater Harvesting: Collecting and storing rainwater (e.g., from rooftops) is a crucial way to conserve water for future use, especially during scarcity. It helps ensure a sustainable water supply. Understanding these concepts helps us appreciate water as a valuable resource and encourages us to use it wisely and responsibly.
Self Study
Image: The water cycle showing evaporation, condensation, and precipitation.
