Sources of water

Water is the most valuable resource, which is fast depleting. 71% of the earth’s surface is water, of which the ocean holds 96.5% of earth’s water. 97% of water is salt water, and 3% is freshwater.

Freshwater is frozen into glaciers and polar ice caps. Freshwater is also found as groundwater. Only a fraction of it is present above ground. This fraction of usable groundwater is a renewable resource.

Before we move on to sources of water, it is pertinent to know the uses of water. Water is used for bathing, cleaning, toilet, food preparation, cooling, fire protection, industrial use, drinking water, or potable water.

Freshwater in useable form is available to us in the way of surface water or groundwater. Surface water is in,

• lakes,
• ponds
• streams
• rivers
• artificial reservoirs or storage reservoirs.

Groundwater is available to us in the form of

• aquifer
• springs
• infiltrations

Rainwater replenishes both surface water and groundwater. Rain is also an essential source of water.

Let us study these sources of water in a little more detail.

Surface water

Though surface water is most abundantly found, all of it is not usable as 97% of it is saltwater. Saltwater is not suitable for drinking. The majority of species on earth are dependant on freshwater for their survival.
Sources of freshwater are rivers, ponds, lakes and artificial reservoirs.

Most of the lakes, ponds, rivers, streams have their origin in glaciers and ice caps. Glaciers are huge masses of ice. These ice caps and glaciers are found on high altitudes where the temperature for most of the year is below the freezing point.

These glaciers and ice caps melt during the summer season and flows as trickling streams. When water flows increases due to massive-scale melting of ice and intermittent rain, it flows in torrents, and that mass of flowing water takes a course with smaller streams joining it forming a river system.

The river is joined by little creeks and streams, which are called tributaries. The river flows through the terrain and finally empties itself into the sea or oceans. Sometimes wind erodes loose soil continuously and causes depression. Precipitation in the form of rain or snow fills up these depressions. Water bodies that are formed are called lakes.

The flow rate in rivers is mostly higher in the spring season, and the flow rate is lower in the winter season. However, this is not the case where the monsoon system is prevalent. Rivers and streams that have their origin in glaciers and ice caps have water throughout the year.

However, rain-fed rivers remain dry during the hot and dry season. They have water only after a monsoon rain.

These natural sources of water are often not enough to meet the ever-expanding need of the growing population. Therefore to mitigate this need, artificial reservoirs or dams are constructed over rivers.

These reservoirs act as sources of water for the community in the watershed area or the catchment area. These reservoirs provide water for irrigation, pisciculture, aquaculture, recreational needs, etc.

Many hydroelectric power stations have been set up on these dams. It provides a clean and renewable source of energy to the population of the catchment area.


Water present under the surface of the earth is groundwater. Hugh reservoir of water is present under the crust of the earth. Water that seeps down the soil and layers of porous rocks collects in large pools.

Groundwater is a renewable, although renewal rate varies according to environmental conditions. Groundwater is rainwater and water from other sources like tap water, which has infiltrated the soil beyond the surface and has collected along with the empty spaces and crevices underneath the earth’s crust.


It is a body of rock and sediment which holds groundwater. There are two types of aquifers-

a) confined aquifer:

when groundwater is over a layer of solid foundation or clay, water is more or less confined to a place where its free movement is restricted. When these are penetrated by well, the water rises because the water in a confined aquifer is under pressure, which is more than atmospheric pressure. These confined aquifers are called artesian wells.

b) Unconfined aquifers:

Here, water seeps from the ground directly above the aquifer. Unconfined aquifers are found below watercourses. Water from these sources flows down to form aquifers. Strata of these unconfined aquifers can be porous rock like limestone, sand, and gravels.

Water from ground reservoirs can be drawn by

a) Open Well

To tap groundwater, sometimes a hole of two to ten meters in diameters is dug deep under the water table to draw out water. The depth of well should be such that even during the dry year, there is sufficient 3 – 4 meters. The water surface in the well and surface water in the soil is at atmospheric pressure.

b) Tube well

A stainless steel tube or pipe is bored into the aquifer to draw out the water in a machine well. One end of the tunnel is fitted with a filter and the other end with a pump that lifts the water.


Replenishment of groundwater takes place through the rain. This system of replenishing water is called the hydrological cycle or water cycle.
The sun’s heat evaporates water from rivers, seas, oceans, and even through transpiration by plants. Evaporated water in water vapor moves high up the atmosphere where it condenses to form water droplets and forms clouds.

When clouds become too heavy to hold any more water droplets, it falls in rain or snow. These together are called precipitation). This rainwater runs off the ground surface as rivers and some percolates down the topsoil to form aquifers. This cycle replenishes the sources of water.

Desalination of seawater though unpopular because of the high cost of treatment is another source of water. Water needs to be judiciously used.


Mike Brown has done Masters in Hydrology and Water Management. He loves coffee and likes to lecture people on climate change. He plays PUBG when he is not working.

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