Irrigation tank

An irrigation tank or tank in India refers to an artificial lake or reservoir of any size. (The word sagar refers to a  large lake, usually man-made). It can also be a natural or spring included as part of a structure. Tanks are part of an ancient tradition of harvesting and preserving the local rainfall and water from streams and rivers for later use, primarily for agriculture and drinking water, but also for sacred bathing and ritual. Often a tank was constructed across a slope so to collect and store water by taking advantage of local mounds and depressions. Tank use is especially critical in parts of South India without perennial rainfall where water supply replenishment is dependent on a cycle of dry seasons alternating with monsoon seasons.

For etymology, see Storage tank.

Tank design
Water is considered a purifying and regenerative element in India, and is an essential element of prayer and ritual. Water is also revered because of its scarcity in western India where dry and monsoon seasons alternate and failure of the monsoon season means famine and death while plentiful water replacing irrigations sources is a time of rejoicing. This resulted in building water storage tanks that combined the practical and sacred. Since ancient times, the design of water storage has been important in India'a architecture As early as 3000 BC  sophisticated systems of drains, wells and tanks were built to conserve and utilise water. Tank building as an art form began with the Hindus and developed under Muslim rule.

An example of the art of tank design is the large, geometically spectacular Stepped Tank at the Royal Center at the ruins of Vijayanagara, the capital of the Vijayanagara Empire, surrounding the modern town of Hampi. It is lined with green diorite and has no drain. The tank was filled by aqueduct.

Village tanks
Ralegaon Siddhi is an example of a village that revitalised its ancient tank system. In 1975 the village was drought-strickened. The village tank could not hold water as the earthen embankment dam wall leaked. Work began with the percolation tank construction by the villagers who donated their labor to repair the embankment. Once this was fixed, the village's seven wells below the tank filled with water in the summer for the first time in memory. Now the village has a supply of water throughout the year.

Kunds
Tanks known as kunds are resevoirs with steps, generally found in South India, and sometimes constructed within the walls of a temple complex.

Bathing in the sacred waters of a temple kund or tank was believed to cure worshippers of afflictions such as leprosy and blindness. Many temple tanks are decaying and drying up today.

Well
In India, a stepwell is a deep masonry well with steps going down to the water level. It is called a vav in west India and a baoli in north India. Some were built by kings and were richly ornamented. They often were built by nobility and were secular constructions from which anyone could obtain water.

Local wells offer water.

Modern tank management
The development of large-scale water management methods and hydroelectric generation have replaced much of the local efforts and community management of water. For example, the state of Karnataka has about 44,000 artificial wetlands locally constructed over many centuries. At least 328 are threatened today.

However, recently a tank regeneration movement initiated by communities and non-governmental organisations (NGO) has arisen. Today, there are approximately 120,000 small-scale tanks, irrigating about 41,200 km² in semi-arid areas of India. This constitutes about one third of the total irrigated land in South India.