India is blessed with numerous streams and river systems with multifarious networks and billions of water bodies and aptly known as the land of lakes and rivers. The country is endowed with plentiful rainfall of ~120 cm/annum, albeit having a non-uniform distribution across various stretches and not distributed throughout the year, as 80 % of rainfall occurs during south west monsoon (four months, June to September ~40 % of the total rainfall occurs just in 2 weeks). Despite substantial water availability, the country faces severe shortages due to lack of traditional water harvesting practices and mismanagement of water and land resources. The country receives ~0.4 billion hectare meter (bham) of rainfall annually (across ~0.33 billion hectares) and varies from 10 cm (Rajasthan’s Thar desert) to 1500 cm (in the Garo, Khasi and Jayantia valleys in Cherrapunji, Meghalaya in the North east). Available per capita water has declined from 9400 m3 (1901), 7000 m3(1941), 3200 m3 (1981) to <1000 m3 (now), seriously impacted the communities life style and the comfort levels in water consumption. The present per capita availability of water is about 10 lpcd (litres per person per day) compared to the minimum requirement by the human body as ~70 lpcd (as per the guidelines of WHO - World Health Organization).
The phenomenon of perpetual and frequent floods and droughts, were addressed through effective harvesting for use during lean periods. For example, Rajasthan meets the domestic water demands despite a very meager rainfall of 10 cm with water harvesting and scientific management.

Indian has been a very self-reliant and independent nation due to the practice of optimal water management and traditional water harvesting systems. Bramha Samhita (Section: Chapter 5 Verses 1, 29 – 56) highlights the importance of water through verses:

This highlights of appropriate water harvesting practices for future use and safeguarding humankind from droughts and water scarcity.
The great civilizations such as Indus-Saraswati Valley (3rd Millennium B.C) have evolved on river banks and contributed to the society’s prosperity through creation of water channels, wells and storage systems for farm utilities and even sewer channels. Great engineering marvels are evident from the existence of interconnected lakes through storm water drains, taking advantages of undulating terrain. The earliest tanks in the form of uniformly built rectangular water storage impoundments were of Harappa and Mohenjodaro civilizations. Many ancient dynasties and rulers (Chola, Satavahana, Chutus, Kadamba, Ganga, Chalukya, Rashtrakuta) have contributed significantly by building the finest of these water harvesting structures based on the region’s topography as well as climatic patterns. Especially the Chalukyas reign is considered as the golden age of tanks due to numerous water harvesting structures - lakes, tanks and canals. During this period, the cascading tanks technique were implemented for flood control as well as irrigation. Water structures at Bagali and Kalyana city are the classic examples of sustainable water harvesting and management. South India witnessed a ‘golden age’ of tanks with a high level of scientific and technical expertise and user friendly sustainable management techniques during 937AD to 1336 AD.
During the medieval period (1300-1700 A.D), the Vijayanagara Empire undertook remarkable, historic and large water harvesting projects. Design marvel of this period, the Sulekere, also popularly known as the Shantisagara  and this water structure is functional still. The construction of tanks evolved and reached a commendable height during the eighteenth century. However, the arrival of colonial rulers led to the downfall of tank systems with the beginning of the British rule and centralized systems of natural resources management.

Practices of local rainwater harvesting, maintenance and management took backseat, during the imperial period (1800 till independence i.e. 1947) of British rule with the push for large scale river valley and canal projects and also due to lack of maintenance and management of small water harvesting structures. Moreover, the natural calamities with frequent floods and famine were responsible for communities being relocated to other localities. Apart from this, high and oppressive taxes and irrigation cess (towards the repair works of these structures) led to the decimation of irrigation tanks during the period of colonial rulers. The Madras high command took several restoration initiatives involving villagers to revive disappearing tanks during 19th century. Thereafter Mysore province, Bombay presidency, Bellary, Hyderabad, Coorg, South Kanara regions could manage the water demand for the irrigation and domestic use with the traditional rain fed and river fed water harvesting structures. Post 1950’s, the country witnessed large scale decline in the tank irrigation systems due to inherited colonial mindset of independent India’s bureaucracy. Deviation from the traditional practices of tank based irrigation systems to channel/well based systems is evident from the decline of 22 %  during 1961- 1981.

There are guidelines for tanks building, their maintenance and troubleshooting right from the Vijayanagar periods, which includes bund design, determining the storage capacity, scientific design of inflows and the outfalls, constructing sluices and waste-weirs etc. In terms of management of the tanks, the practice of an annual de-silting involving all sections of the community, which helped in developing the socio-cultural understanding and a unified community. However, with the construction of huge dams and large scale diversion of flood waters led to the crippling of incentive based process of tank management and the communities completely lost their roles in realizing that the tanks and the water bodies are their assets and moreover their construction and maintenance in entirely their responsibility. This necessitates to bring the awareness and reformations so that local people can assume ownership and responsibility of water harvesting structures. The financial wellbeing of the region depends on the water availability and judicial use, mentioned in “Arthashastra” and “Kunala Jataka”. The scriptures also highlight of an economic structure for a proper regulation of water where the financial requirements for constructions were met by the public-private investments. During the Mauryan period itself, there were charges for water use that has been followed till today as water surcharges. 
Deterioration of traditional water harvesting practices has resulted in the inequity in water distribution and growing water scarcity, which has escalated water conflicts during the 20th century. Irresponsible management of natural resources is evident from

• sustained inflow of untreated sewage and industrial effluents;
• dumping of solid waste (with 70% being organic); and
• transport of untreated wastewater in storm water drains (water drains are essentially arteries of a landscape supposed to carry rain water to water bodies)

Due to these unauthorized practices, vital constituents of the landscape (wetlands and drains,) have become breeding ground of disease vectors, stinking cesspools and emitters of GHG’s (methane, carbon di-oxide, etc.), etc. These practices are posing serious threat to public health and hygiene with an irrecoverable loss in aquatic biodiversity. Unplanned and un-coordinated rapid urbanization has further stressed the natural resources in the region. The water demand of the urban conglomerates is met with piped water supply or from water transported from distant areas. Coupled with this, substantial degeneration of the traditional knowledge has resulted in deterioration of tank management practices. Sustainable water management of water resources through revival of traditional water harvesting strategies and comprehensive watershed restoration and management by involving local stakeholders is essential for adequate groundwater recharge for maintaining regional water balance in the region.

Table 1.1 details major water harvesting endevours undertaken since 3rd millennium BC. Global warming and consequent changes in the climate with highly un-reliant rainfall and consequent water scarcities have already pushed the federal governments to undertake drought protection initiatives through combined efforts of the communities to safeguards tanks and lakes in the regions. Though, harnessing and supplying water is the sole responsibility of the government, active public participations will ensure sustainable management of natural resources. Earlier decision makers of the princely states were successful in developing minor irrigation systems, appropriate watershed management and efficient water harvesting strategies. Rulers provided the resources to construction and continued operation of water bodies, while the local community’s aided in building, maintaining, managing and optimal distribution of water. The centralized irrigation systems coupled with increased incidences of untimely rainfall and higher temperature, lack of annual maintenance, deforestation in the catchment and receding community participation, led to the decline of thousands of traditional water harvesting systems. As a consequence of these, the thousands of lakes and tanks are silted with the decrease in the overall storage capacities and groundwater recharge. Unplanned urbanization has led to the increase in urban conglomerates, with drastic reduction in land cover of the catchment, which substantially reduced the water holding capacity of the catchment. Higher incidences of flooding and soil erosion, is the direct consequence of damaging the water harvesting structures. Therefore, it is necessary to inculcate the traditional knowledge on sustainable water harvesting and management practices in the educational curricula. At a village/ward level it’s necessary to identify the appropriate investment strategies and make the local Panchayats/ward member responsible for the operation and maintenance of the tanks. This will help in adopting the decentralized water harvest and management practices in the arid and semi-arid regions that are economical and technically feasible alternative to big dams and reservoirs.

Table 1.1: Chronicle of water harvesting structures

Archeological evidences indicate that tank systems (1st century B.C.; region where lord Sri Rama began his exile), were brick lined structures with impoundment capacity of ~260 m length, ~20 m wide and ~3 m depth,. These cascaded tanks were along the natural gradient/slope from river Ganga towards the downstream region. The water from the river has been drawn in stages and is initially made to pass through two deep earthen tanks to arrest turbidity and solids (settling tanks - for silt capture) and the overflow passing to the subsequent ponds. These cascaded ponding systems - series of ponds systems through step wise treatment aided in providing uncontaminated water to the dependent families. The inlets to the main tank have provisions for ramps (steps) with curved edges which aided in reducing the velocity of the water. A series of wells were created intermittently in the tank bottom to evade water scarcity during the dry periods.

Means and measures for sustainable water harvesting: Sufficient provisions were made through tank systems for capturing rain water, land run off and the surplus floodwater from the rivers and streams. The various water harvesting structures were built for capturing rainwater and in the path of stream/runoff, besides capturing the flood waters. These structures design were based on the various climatologic, bio-geographic and topographic elements (Table 1.2, Table 1.3)

Table 1.2: List of Bio-geographical elements and rainwater harvesting approaches

Advantages of traditional water harvesting structures are:

• water made to stand for a period so as to allow infiltration / percolation and recharging of groundwater aquifers to sustain good water levels in the surrounding wells;
• a saturated sub soil/top soil, enhances the green cover in the surroundings;
• green cover in the catchment reduces soil erosion and hence sedimentation of rivers; and
• mitigation of instance of floods and runoff.

Tank irrigation system is one of the important and oldest sources of irrigation in India. Southern parts of India, where average rainfall is around ~70 cm, decntralised water harvesting was practiced, evident from the existence of ~127,000 tanks - Andhra Pradesh, Tamil Nadu and Karnataka states. Optimal water harvesting through cascaded tanks was initiated during Sangam Period (300 B.C.), to address acute scarcity of water for domestic and irrigation purposes.

Water harvesting and storage in Deccan Plateau, the peninsular India: The elevation of Deccan plateau ranges from 1000 m in the south to 500 m in the north, with a low to moderate rainfall. This necessitated adoption of irrigation systems like tanks, ponds, lakes, embankments across rivers and streams, reservoirs, etc. in the semi-arid belts. Check dams or diversion weirs were built in these regions across rivers in the sates as Maharashtra, Andhra Pradesh and Karnataka. Due to damming, the water levels in the flow courses get raised and thus they were made to flow into channels for irrigational and other essential requirements. These novel temporary storage systems across a small stream, helped in sustaining the water during lean periods for irrigation, etc. Kere (large tanks) in Karnataka and cheruvu in Andhra Pradesh fed by streams, were the main irrigation source in places, where the average rainfall varies from 100-1000 cm. Anicuts were built across many rivers. Chain tanks were built in hilly regions with wide valleys. Several tanks were constructed starting from foothills to the floor of the valley. Interconnected drains in the basin take the overflow from one to the next.
Especially in Karnataka the tanks are known as kere were the predominant traditional methods of irrigation in the central Karnataka plateau region. They were fed either by channels branching off from anicuts “anekattu in kannada” (check dams) built across streams, or by streams in valleys. The tanks were built in series, so that overflow from one tank to the next in the course of the stream.
Tanks and lakes/water bodies are the oldest source of water for irrigation in the southern part of the country. There are millions of water bodies all over India. They are a sort of small reservoirs with earthen walls, used for storing water diverted from a stream or run off. The tanks and lakes for the irrigation purposes in India are mostly concentrated in South Central Karnataka, Telengana and Eastern Vidarbha; Coastal Tamilnadu and Andhra Pradesh and to lesser extent in Rajasthan, east of the Aravalli mountains. These tanks or reservoirs are the most important source of irrigation in South India. Several ancient tanks are found here.

• Pampasagar tank in Bellary district near Tuungabadra river
• A series of tanks at different levels of a watershed (1096 A.D.) at Kattagiri
• Pakhal, Ramappa, Laknavaram and Sanigaram in Warangal and Karimnagar districts of Andhra Pradesh (12th and 13th centuries A.D.)
• Varthur and Bellandur kere, 1000 years old constructed by Ganga kings

Table 1.4: Emergence and decline of decentralized water harvesting structures

The tank systems are a decentralized means of water supply and irrigation that also helps in flood control, managing drought and maintaining the water table of the region, aquaculture and fisheries, maintaining a green belt as the riparian vegetation. In Karnataka the tanks have been variably named as katte, kere, and kunte that can be rain fed, stream fed or fed by both. These tanks or kere essentially comprise of features as a watershed/catchment area, immediate tank bed, the downstream command area, the bund, adjoining canals, sluices for controlled release of water to downstream and weir over which the balance of the overflow passes. Appropriate institutional backup, awareness among public about socio-cultural practices would help in safeguarding these tank systems.
Studies have revealed lakes or tanks were adopted in drier belts where there are no other sources of water or river were non-perennial. These water bodies apart from recharging groundwater resources helped to meet both the domestic and irrigational requirements of the region. The southern India as well as the arid areas of central and western India have seasonal rivers which limit the scope for canal irrigation while the scope for wells is limited due to the presence of hard granite and gneisses. As a result of these, tank irrigation gained prominence in these areas.
The tank irrigation systems are the typical example of the water harvesting techniques and are mostly managed by the local communities as common property resource. The disappearance of the age old traditions of tanks (Table 1.4) is due to the adoption of colonial style of lake management with the lack of annual maintenance and non-participation of all stakeholders. Financial constraints, lack of incentives and poor community participation have made the tank based system unsustainable.
Some of the contemporary approaches to harvest rain water are construction of check dams in small streams so as to retain water (required for the lean period). Advantages with these water retaining structures are (i) retarding the velocity of water, (ii) arresting soil erosion, (iii) enhancing soil moisture and (iv) percolation / infiltration, recharging the aquifers. The other designs include contour trenches that are basically dug on hill slopes and barren unused fallow lands (with riparian vegetation along the bank) for soil conservation through retention of soil moisture. This helps in checking the velocity of the surface runoff and these regions with the slopes are later used for planting trees. Bunds i.e. little earthen barrier are made on the slope between the agricultural land. The entire slope is transformed into several short ones that first of all increase the standing time of rainwater allowing frequent percolation and secondly it checks the velocity thereby reducing the soil erosion occurring through runoff. This also aids in diverting the runoff- i.e. the excess water for the purpose of water harvesting.
One of the other essential architecture is the contour stonewall that are often constructed across a hill slope to interrupt the runoff. This also helps in reducing the soil erosion and provides with greater standing water for adequate water percolation. With the help of these structures sub-surface dams / groundwater dams are build that checks the natural flow of groundwater and stores it. This maintain a balance during monsoon and also in the dry season. Underground storage of water helps to evade evaporation losses and also safeguards the water from external pollutants and contamination from pathogens.
Percolation ponds or Jaldhar model (in the eastern highlands) are similar to irrigation tanks and have demarcated bunds that avoids water to spill over and is orderly allowed to release the surplus water through the waste weir. The rainwater is harvested in a small portion of the farmland at the lowest elevation (mostly in one corner of the land) helps in the subsurface and storage. The practice of networking of farm ponds has been in practice in Karnataka, evident from the existence of interconnected >300 farm ponds along the contour lines in the undulating terrain of Adihalli watershed, Arsikere taluk of Hassan district. This provision allows easy access to water, equitable distribution and retention of substantial soil moisture. This not only helped in meeting the domestic and the irrigational requirement of the region, but also created an ambient microclimate in the region, with improved water balance and adequate ground water recharge.
A well known success model of lake ecosystem is at Jakkur in Bangalore with integrated wetlands ecosystem. Complete removal of nutrient and chemical contaminants happens when treated sewage (secondary treated) passes through constructed wetlands and algae pond, due to bio-physical and chemical processes (Ramachandra and Mahapatra, 2015). The water in the lake is almost potable with minimal nutrients and microbial counts. This model has been running successfully for the last 5 years after interventions to rejuvenate the lake (Ramachandra et al., 2013). This systems is one of the self-sustainable way of lake management while benefitting all stakeholders - washing, fishing, irrigation and local people. Wells in the buffer zone of 500 m have higher water levels and without any nutrients (nitrate). Compared to the current status, groundwater quality assessment before rejuvenation of Jakkur Lake had higher nitrate values.  Adoption of this model also ensures nutrient free and clean groundwater, which helps in achieving the goals of providing clean water to the local community.

Another very good example of constructed water body is of the centenary pond at IISc, created solely to harvest rainwater. Taking advantage of undulating terrain in the campus, storm water drain is routed to a low lying area. The spatial extent of the water body is about one hectare and stores on an average 0.1 million lakh liters. This water body is now an abode of a variety of aquatic animals and has been an attractive to several resident and migratory birds. The creation of these water bodies has helped in a good ambience and maintaining a good biodiversity in the region besides providing a very good aesthetics and is a now a means of stress relief for the students learners of higher education. These successfu experiments highlight that water quality can be maintained to meet the local requirements by optimal management of bio-physical dynamics in a water body.