Groundwater
Groundwater is our primary source of drinking water. About 85% of drinking water in India and 60% of water for irrigation comes from groundwater.
Water seeps into soil from rain, melting snow or farmland irrigation, and gets collected underground. Below the ground there are different levels of water saturation. Closer to the surface, the gaps between the soil and rocks are filled with air and water. The deeper you go, the less air and the more water there is. The line below which there is no longer any air but only water is called water table. Underneath the water table, all available space is filled with water.
The body of soil and rocks under the water table is called an aquifer. Groundwater fills all areas of the aquifer until it reaches the impenetrable rock at the bottom. It is like a container for groundwater. The Great Artesian Basin in Australia is the biggest known aquifer. India contains 14 principal aquifer systems and 42 major aquifers, including the Indus Basin, the most important cross-country water source.
Dry land like deserts have a lower water table, whereas places with heavy rainfall have higher ones. The height of the water table decreases in summer due to evaporation, whereas in monsoon or early spring, the height of the water table increases. If the water table rises high enough to touch the surface, it becomes a spring, a lake or a river.
To extract water, wells are dug through the water table. If given enough time for the aquifer to replenish itself, the well will keep supplying water. However, over-extraction can exhaust groundwater fairly quickly. The sensible management of these aquifers and groundwater is necessary if we want to preserve the water table. Water is a vital resource and like oxygen, life would be impossible without it.
