Groundwater, located beneath the earth's surface in soil porespaces and in the fractures of rock formations, isa natural storage of rainwater that can be accessed at any time. A unit of rock or an unconsolidated deposit is called an aquife rwhen it can yield a usable quantity of water. Groundwater is recharged from, and eventually flows to, the surface naturally; natural discharge often occurs at springs and seeps, and can form oases or wetlands, emerges out of the ground surface. Depth to groundwater or the water table depends on hydrogeology of the ground and needs to be understood for sustainable management of groundwater.

Groundwater, which forms an important source for drinking purposes, is often withdrawn for agricultural, municipal and industrialuse by constructing and operating extraction wells. Extraction of water requires energy. In the olden times when the source of power was limited to animal irrigation with groundwater was limitedgroundwater was rightly considered as an abundant resource, since the withdrawals were less than the recharge of groundwater.In South Asia, inexpensive treadle pumps have been successful in extracting irrigation water from shallow aquifers, allowing farmers to make good use of the household labour and increase production and income.With the advent of fossil fuels, use of mechanised pumps, and wide distribution of electricity, particularly in semi-arid regions, the groundwater provides an opportunity for equitable growth through irrigated agriculture.

Over-use, oroverdraft, has resulted in continuous lowering of water table, amounting to mining of groundwater and resulting in major problems for human use as well as to the environment such as groundwater-related subsidence and saltwater intrusion.

Importance of groundwater to ecosystems to sustain rivers,wetlandsandlakes, as well as subterranean ecosystems withinkarstor alluvial aquifersis not fully understood and is often overlooked.‘Groundwater recharge', that involves capturing rainwater that would otherwise run-off, and using it to refill aquifers is a possible solution. However, such a recharge should be based on the understanding of the hydrogeology and full caution against potential of polluting groundwater. Movement of water and dispersion within the aquifer can spread the pollutant over a wider area, which can then intersect with groundwater wells or daylight into surface water such asseepsandsprings, making the water supplies unsafe for humans and wildlife. Presence of natural impurities in groundwater such as Arsenic in Bangladesh, and other parts of the world, in water used to grow crops could degrade soils, reduce yields – and find its way into food.

Today, more than 30% of irrigated areas around the world sources groundwater, particularly in China, India, Pakistan and Mexico. At the same time due to over exploitation of groundwater beyond the recharge capacity and the continuous lowering of water table large chunks of energy is being consumed making groundwater irrigation unsustainable in the long term. Groundwater management principles need to be evolved based on scientific assessments, institutionally and legally supported, and implemented by empowering various stakeholders.