Water is the most common and important substance around us. Water is essential for almost every task we perform on a daily basis as well as for agriculture and industries.
- All animals and plants need water. The human body has about 70 percent water by weight. Similarly the elephants and plants have 80 percent and 60 per cent water by weight respectively.
- Animals drink water from ponds, streams and rivers. Plants take in water from the soil through their roots. From the roots, it goes to different parts of the plant. The plant uses this water for its life processes. It also loses water continuously from the tiny openings in the leaves. The process is called transpiration.
- Seeds cannot germinate without water. Water helps animals in releasing heat which maintains their body temperatures.
- A villager in India uses about 12 litres of water every day. In cities, a person uses 50-2000 litres of water every day. With the rising living standards, the requirement of water has also increased.
- Large amounts of water are consumed in agricultural activities. Many industries such as paper, rayon, petroleum refining, fertiliser, dye, drug and chemical industries require large quantities of water.
- In some countries, people use water to warm their houses. It is used to keep things cool. A car radiator is filled with water to keep the engine cool.
- The largest amount of water on the Earth is in oceans. The oceans cover more than two-thirds (2/3) surface area of the Earth. Seawater is salty and cannot be used at home and in agriculture. So, we depend upon other sources of water like springs, rivers, lakes, ponds, wells, rain, snow and underground water. Water obtained from these sources is not always fit for drinking and cooking purposes. Many impurities and germs may be present in it.
- Various methods are used to make this impure water fit for drinking. People in cities get pure water from taps. This impure water travels a long way to reach the taps. In many cases, water is first pumped from a source, such as a river or lake, and collected in a reservoir. Then it goes to the waterworks where it is cleaned. Here, it is filtered through layers of gravel and sand. The dirt stays behind in the sand, then water is treated with some chemicals like chlorine to kill the germs. The clean water is supplied through main pipes to different parts of the city. Smaller pipes take the water to each house.
At places where tap water is not available, people draw out water from rivers, lakes, springs and wells. Water from these sources should be made fit for use by boiling, filtering and treating it with some chemicals such as potassium permanganate.
- Pure water is colourless, odourless, tasteless and transparent. Small quantities of dissolved salts and gases give a pleasant taste to water. Water from the wells, tube wells and taps have dissolved substances in it.
- Water containing large amounts of dissolved salts is called saline water.
WATER CYCLE IN NATURE
- The Sun provides the heat energy to the water in oceans, ponds, lakes and rivers leading to its evaporation into the air continuously. The radiating heat warms up the air closer to the surface of the Earth. This makes the warm air lighter. Therefore the air containing water vapour rises. Temperature decreases with increasing height in the atmosphere.
- Minute water droplets are formed when the water vapour cools at higher altitudes. These water droplets form clouds. Minute water droplets form drops of water which may fall as precipitation. Water droplets freeze into snow particles when the air cools further. These particles join together to form snowflakes which falls as snow in colder regions.
- At some places during winter, snow falls. When it melts, water flows into streams and rivers. Many of these rivers fall into the ocean. Most of the water falling in the form of rain also reaches the sea through streams and rivers.
- A part of the rainwater evaporates. A part of it is absorbed by the soil and goes underground. Water on the land is utilised by living things, including human beings, which also comes back to nature through various life processes. The water cycle occurs in nature all the time.
HARD AND SOFT WATER
- When water does not form lather with soap easily due to presence of some types of salts dissolved in it, it is called hard water. Water which forms good lather with soap easily is called soft water.
- The presence of calcium chloride and magnesium chloride in water makes it hard.
- The hardness of water can be removed by boiling it or treating it with chemicals such as washing soda.
Note: Hard water is suitable for drinking but not for washing clothes because dirt cannot be removed easily in it.