NCERT Notes for Class 8 | NCERT Quiz | NCERT Standard 8 - Science


Chapter 16 : Water

World Water Day : 22 March is celebrated as the  world water day.The General  Assembly of the United Nations proclaimed the period 2005 – 2015 as the International Decade for action on “Water for life”. All efforts made during this decade aim to reduce by half the number of people who do not have access to safe drinking water. The amount of water recommended by the United Nations for drinking, washing, cooking and maintaining proper hygiene is a minimum of 50 litres per person per day. This amount is about two and a half bucket of water.

Water Cycle : When water circulates through the water cycle it can be found in all the three forms, i.e., solid, liquid and gas —at any given time somewhere on the earth. The solid form, snow and ice, is present as ice caps at the poles of the earth, snow-covered mountains and glaciers. Liquid water is present in oceans, lakes, rivers, and even underground. The gaseous form is the water vapour present in the air around us. The continuous cycling of water among its three forms keeps the total amount of water on the earth constant even when the whole world is using it.

Water Table : If we dig the soil deeper and deeper, we would reach a level where all the space between particles of soil and gaps between rocks are filled with water. The upper limit of this layer is called the water table.The water found below the water table is called groundwater.

Aquifer : The rainwater and water from other sources such as rivers and ponds seeps through the soil and fills the empty spaces and cracks deep below the ground. The process of seeping of water into the ground is called  infiltration. The groundwater thus gets recharged by this process. At places the groundwater is stored between layers of hard rock below the water table. This is known as an aquifer.

How water is replenished  : Water drawn from under the ground gets replenished by seepage of rainwater. The water table does not get affected as long as we draw as much water as is replenished by natural processes However, water table may go down if the water is not sufficiently replenished. This may happen due to many reasons. Increase in population, industrial and agricultural  activities are some common factors affecting water table. Scanty rainfall is another factor that  may deplete the water table. Yet another factor affecting water table could be deforestation and decrease in the effective area for seepage of water

Water harvesting : The rainwater can be used to recharge the groundwater. This is referred to as water harvesting or rainwater harvesting. It has been suggested that we should plant eucalyptus trees all along sewage ponds. These trees absorb all surplus wastewater rapidly and release pure water vapour into the atmosphere.

Vermi cakes : A design of a toilet in which humans excreta is treated by earthworms has been tested in India. It has been found to be a novel, low water-use toilet for safe processing of human waste. The operation of the toilet is very simple and hygienic. The human excreta is completely converted to vermi cakes — a resource much needed for soil

“No one need to wait for anyone else to adopt a humane and enlightened course of action."

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