Groundwater is the largest available freshwater resource on earth. It serves the drinking water needs of nearly half of the humanity, including almost everyone who lives in rural areas. The largest use for groundwater is to irrigate crops. In India, about 90% of groundwater is consumed by irrigation alone. At 250 billion cubic meters per year, India is the world’s largest user of groundwater. Yet, the subject is poorly understood. Whenever a group of attendees at an explanatory session on groundwater is asked to describe what they learned, their individual answers grossly vary. Groundwater can be protected only when it is understood.
Simply said, groundwater is the water found beneath the ground. It is mostly an invisible entity, except at the point of intersection e.g. a dug well, or the leaking walls of a freshly cut hill slope. Since groundwater is not visible to naked eyes, groundwater resources are often subjected to unscientific extraction and over-exploitation. The process of formation, availability and the fugitive nature of groundwater is fascinating and warrants better understanding.
Formation of groundwater
When water from fresh precipitation (rain or snow) is incident on the surface of the ground, a portion of the water infiltrates into the unsaturated zone of soil. Depending upon local geology, the infiltrated water may percolate deeper to occupy the natural cracks and spaces in the soil, sand and rock. The room available for water to accumulate into a more or less contiguous saturated zone is called an aquifer. As the aquifer reaches saturation, any additional percolation moves the water slowly across the geologic formations of soil. Such underground flows are a factor of gravity; the nature of the local geology; and the extent of saturation of water. Aquifers are the net volumetric space that can hold water. Although these are but a sum total of cracks and voids in the ground, and necessarily hidden, it is possible for modern science to closely estimate their capacity and ability to receive, hold and deliver groundwater. Over the past decades, hydrogeologists have combined modern scientific techniques and traditional wisdom to keep perfecting the locations, capacities and also the types of aquifers.
The part of incident water which cannot infiltrate into the ground, flows away in the direction of the slope of the surface. Such a flow is called run-off. The percentage of precipitation that flows away is the coefficient of run-off. A hard-paved concrete surface will typically have over 95% run-off coefficient. In contrast, pristine forest soils or grassy terrains typically have negligible run-off. The amount of infiltration can vary through the year, depending upon the seasonal saturation of the soil. When such a flow of surface run-off is blocked for any reason, it will accumulate and cause inundation and flooding.
Recharge
As aquifers are merely voids in the earth, they can be filled with water to different capacities, get depleted, or even be empty. The process of filling up of aquifers is recharge. Groundwater is naturally recharged by precipitation, but only to the extent permitted by the local topography and the underlying geology. In other words, the quantum of infiltrated water reaching the saturated zone is different for different soil types. Furthermore, all the infiltration in a particular area does not necessarily add up to water available in the immediately underlying aquifer. Aquifers could reside at large, seemingly unlikely, distances from the location of recharge. It warrants therefore to identify good groundwater recharge zones, and not casually infer about the location and capacity of an aquifer in the proximity of recharge. It is also important to know that the amount of rainfall in a given season cannot be regarded as a flat multiplier of the amount of groundwater recharge achieved. Often, in poor recharge zones, heavy precipitation can mean more floods, followed by droughts in the post-monsoon season. Equally well, some apparently arid regions show remarkable groundwater potential in spite of low rainfall.
When large volumes of storm water infiltrates into the ground, it is likely an invisible gain to groundwater. In contrast, a flood may be termed as a visible failure to recharge.
Discharge
Springs emerge when a saturated aquifer bleeds out of cracks in soil. Groundwater residing in and moving across host aquifers can get discharged through springs, lakes, rivers, streams, or man-made wells. Some of the largest of the world’s rivers are natural springs at their origin. The constant flow of a spring forms a stream, carving its own channel in the topography, and moving downward in the watershed as surface water. When multiple streams converge, they form a higher order stream. Successively higher order streams eventually converge into larger flows that make a river. But all springs that contribute to the flow in a river may not be visible. The banks of a river are live interchange zones of groundwater and surface water. When the water table is above the flow in the river, groundwater emerges as springs and adds to the flow of the river. Conversely, when there is more flow in the rivers and the water table falls under, e.g. in the early monsoon season, the interchange zone may facilitate recharge of the connected aquifers. It explains thus that extreme rainfall events later in the season can cause worse floods, because the related aquifers may be left with little or no capacity to absorb floodwaters.
Generally poor understanding of groundwater derives from its assumed intangibility and invisibility. This aspect often plays a truant on unsuspecting engineers, economists and urban planners. Many large water management bodies, dam authorities and municipalities tend to ignore groundwater in their macro planning. Groundwater and surface water administrative authorities can lead to avoidable dissonance and costly misgovernance. Around 2018-19, ACWADAM, a Pune based groundwater advocacy and research organisation, studied and published Pune’s aquifer maps (click to download). The study demonstrated that groundwater made up nearly a half of the city’s urban water. This brought the subject of groundwater into mainstream conversation. As a result of the findings, the Pune Municipal Corporation constituted a groundwater cell in 2019 to address the city’s water planning more comprehensively. As of 2025, the idea of a dedicated groundwater monitoring task force has still not occurred to most municipalities in India. Much water still needs to flow down this stream of thought.
Various state governments across India have been rolling subsidies on solar groundwater pumping solutions to ease farm-level water stress. Solar pumps could mean an unchecked abstraction of groundwater, as no direct energy costs have to be borne. The latest state-push for ethanol blending of petrol has already triggered a shift towards more water-intensive corn and sugarcane. cropping. Together, this could translate into a runaway disaster for India’s groundwater and the entire policy needs a careful, responsible and comprehensive rethink.
Chart credit: Girdhari Lal Meena, © 2018 IJRTI | Volume 3, Issue 3 | ISSN: 2456-3315
More information on groundwater, aquifers, aquifer-types, rainwater-harvesting and urban-flooding is covered as separate articles connected to the respective links.
Further reading:
* The Groundwater Foundation website has many useful resources
https://groundwater.org/what-is-groundwater/
* Wkipedia Page covers the many aspects of groundwater, uses, resources and aquifers in the classical encyclopedic format:
https://en.wikipedia.org/wiki/Groundwater
* The pdf published on the National Institute of Open Schooling Project (NIOS) website has a Notes and Q & A format and covers the aspects of artificial recharge of aquifers and depletion of groundwater:
https://www.nios.ac.in/media/documents/333courseE/28.pdf
* Groundwater FAQs on USGS website:
https://www.usgs.gov/faqs/what-groundwater
* The Environment Protection Agency (EPA) has a summary pdf covering how aquifers fill up and the causes and precautions against groundwater contamination:
https://www.epa.gov/sites/default/files/documents/groundwater.pdf