What are the Different Sources of Water
Precipitation in the form of rain or snow provides fresh water to our planet Earth. Most of the fresh water returns to the oceans through rivers flowing across the globe. A small portion of it is absorbed by the soil and is stored underground. A still smaller portion is stored in natural (lakes and ponds) and man-made (tanks and reservoirs) water bodies. Thus, the various sources of water can be divided into two main categories:
- Surface water
- Underground water or subsoil water
Surface Water
Water present on the surface of the Earth is called surface water.
It can further be classified into three categories depending upon the ‘purity’ of water.
Rainwater: Rainwater is the purest form of water. Why? As water from the seas and rivers evaporate to form water vapour under the heat of the sun, it leaves behind all the impurities. When precipitation occurs, the first showers dissolve certain gases present in air and also bring suspended impurities along with it. Subsequent showers, however, consist of pure water.
River and Lake water: The water in these water bodies comes either from rainfall or melting of snow (glaciers) on the mountains.
Sea and Ocean water: Oceans are a huge store of water. Millions of litres of water is present in them. But the water is salty and is not fit for either domestic or agricultural use.
Underground Water or Subsoil Water
Groundwater is the water under the ground where the soil is completely filled or saturated with water.
Rainwater seeps through topsoil and layers of rocks like limestone, sand and gravel, and gets collected on top of non-porous layers. The top level of this underground water is called the water table. Underground water is also known as an aquifer.
The place where the water table meets the land surface, water may come out of the surface in the form of a natural spring and flow into a lake, stream or an ocean. Groundwater that meets the land surface also keeps rivers, streams, and lakes filled with water. Wells can also be drilled to take out the underground water.
