3. Highlights of the survey
i) The global distribution of fresh water (less than 3% of total quantity of water) of which annually 20% is available in liquid form.
About 98.4% of this is, in the form of ground water, 1% is in the lakes. The rivers and atmosphere contain 0.1% each while solid body carries 0.2% and the rest negligible amount is considered as biological one.2 For India, the water budget reveals that out of a total water input of 420m. ha m received annually through precipitation ad river flows from outside the country, 70 m. ha m evaporates immediately, 165m. ha infiltrates into the soil and 135 m. ha m remains as surface water in rivers, ponds, lakhs etrc.2 Only 50 m. ha m is available in the form of ground water. An estimated 150 m. ha m of water flows into the sea or to other countries like, Bangladesh and Pakistan.2 Most of the rainfall (over 57%) in the country is received during the south-west monsoon period.
Water resources are required to be handled carefully for their sustainable development. Ground water is an important source of fresh water. Quantum of water that can be extracted economically from ground water aquifers every year has been estimated as 450 km3. Therefore, on an average about 1140 km3 of water may be reckoned as available for exploiation.4
ii) The present (1990) total demand of water for drinking, irrigation, industrial and energy uses is 552 km3 and is expected to increase to 750 km3 by 2000 and to 1050km3 by 2025 (table 1.1.).
iii) There is a large variation in rainfall from region to region, season to season and year to year. Nearly 9% area of the country is arid and 40% is semi-arid (annual rainfall between 500 & 1000 mm)4. Because of the vagaries of the monsoon, semi-arid regions of the country are drought prone.
iv) The National Water Policy enunciates that water is a scarce and precious national resource to be planned, developed and as such conserved, on an integrated and environmentally sound basis. The concept of transferring water from a surplus basin to a deficit basin has been under consideration by water resource planners in the recent past. The policy emphasizes the need for an integrated and multi-disciplinary approach for the planning, formulation, clearance and implementation of projects.
Water resource management for its optimum use is multi-dimensional. This study gives an account of rain water harvesting technologies for domestic and agricultural applications through low investment schemes and artificial recharging of aquifers.
v) Ponds, Nadis, Talabs, Haffirs, impounding ponds etc. are age old practices of rain water harvesting and storage for various purpose such as drinking, washing, irrigation, industrial uses and power generation.
The varied versions of techniques like roof-top harvesting have been primarily used for drinking purposes and the runoff inundation methods like khadins, ahars, submerged tanks, embankments, and farm ponds have been primarily used for agricultural purposes.
It would be wrong to make too sharp a division between domestic and agricultural applications, or between roof and ground surface catchments. All of them have been put to alternate or multiple uses.
vi) Traditional water harvesting systems are not only relevant, but are necessary and in some cases vital today. Some of these systems were in fact neglected when more attractive systems were installed b the government agencies. However, the failures of modern systems have resulted in attempts to regenerate and multiply the traditional ones. These efforts have not been entirely successful due to several reasons including that there is no clear policy regarding traditional water harvesting systems.
vii) Water harvesting techniques have several advantages: they serve local communities, they can be built with local material and skills in a short time. They however, face several problems, the important ones are silting, breaching, seepage, evaporation and submergence of cultivable lands. The technical solutions to these problems have been discussed in the report. Back