Water is essential for all forms of life. Every living organism, from the smallest microorganism to the largest animal and plant, needs water to survive. Our body itself contains about 70% water. Water is used for drinking, cooking, bathing, growing crops, in industries and in many other activities. Without water, no life would exist on Earth. In this chapter we study the water cycle, the sources of water, and the urgent need to conserve this precious resource.
Although about three-fourths of the Earth's surface is covered with water, most of it is saline sea water which is not fit for drinking. Only a small fraction of the Earth's water is fresh water available for use. As the human population grows and industries and agriculture expand, the demand for fresh water increases, while the sources of fresh water are limited. Therefore, water conservation has become a matter of great importance.
The water on the Earth keeps moving from one form to another through a process called the water cycle. The sun's heat causes water from oceans, rivers, lakes and soil to evaporate into the air as water vapour. This rising vapour cools and condenses to form tiny water droplets that make up clouds. When the droplets grow large enough, they fall back to the Earth as rain, snow or hail. This is called precipitation.
The rainwater flows into rivers, lakes and oceans, and also seeps into the ground to become groundwater. Some of it evaporates again, and the cycle continues. The water cycle is a continuous process driven by the sun's energy, and it maintains the supply of fresh water on the Earth. The changing states of water - evaporation, condensation and precipitation - are all part of the water cycle.
Water on the Earth is found in many sources. The main natural sources are rivers, lakes, oceans, seas and glaciers, along with underground water. Surface water includes water in rivers, lakes, ponds and oceans. Groundwater is the water that seeps into the soil and collects in the spaces between rocks and soil particles; it is obtained from wells and tube wells.
The underground water is a very important source of fresh water. Rainwater seeps through the soil and rocks and accumulates in the deeper layers of the Earth. This water is used for drinking, irrigation and other purposes. In some areas, groundwater is found very close to the surface, while in others it is deep. The level at which the groundwater is found is called the water table. The water table is not fixed; it rises after heavy rainfall and falls in dry seasons.
Increasing population, expanding agriculture and industrial growth have led to a great demand for water. As a result, groundwater is being used up faster than it is being replenished. In many areas, the water table is falling at an alarming rate. In addition, natural water sources are becoming polluted by domestic and industrial wastes, making the water unfit for use.
Several factors cause water scarcity. Excessive use of groundwater through deep tube wells, deforestation, and concrete surfaces that prevent rainwater from seeping into the ground all contribute to the depletion of groundwater. When rain falls on roads and buildings, it quickly flows away instead of soaking into the ground, reducing the recharge of groundwater. Deforestation also reduces the soil's ability to hold water. As a result, many regions face severe water shortages, especially in the dry season.
We must conserve water and use it carefully. The process of making rainwater seep into the ground is called rainwater harvesting. In rainwater harvesting, rainwater is collected from rooftops and open areas and directed into the ground through pipes or pits so that it can recharge the groundwater. This simple technique can raise the water table and prevent water shortage.
We can conserve water in many simple ways in our daily life. We should not keep taps running while brushing teeth or washing clothes, we should repair leaking taps and pipes, use water in a bucket for bathing instead of a shower, and wash vehicles with a limited amount of water. Wastewater can be treated and recycled for use in gardening, washing and industrial processes. Industries and households should minimise water wastage and reuse water wherever possible. By using water wisely, we can ensure that this precious resource remains available for future generations.
| Step of Water Cycle | Process |
|---|---|
| Evaporation | Sun heats water, it becomes vapour |
| Condensation | Vapour cools and forms clouds |
| Precipitation | Water falls as rain, snow or hail |
| Water Source | Type |
|---|---|
| Rivers, lakes, ponds | Surface water |
| Seas and oceans | Saline water |
| Wells, tube wells | Groundwater |
| Glaciers and snow | Frozen fresh water |
Water is a precious and finite resource that supports all life. The water cycle, driven by the sun's energy, continuously recycles water through evaporation, condensation and precipitation, providing us with fresh water. The sources of fresh water, especially groundwater, are limited and are being depleted by overuse, pollution and deforestation, leading to water shortage in many regions. Conservation measures like rainwater harvesting, fixing leaks and recycling wastewater can help preserve water for the future. By using water wisely, we can protect this vital resource for generations to come.