'Yaapo divyaa utavaa sravanti khanitrimaa utavaa yaa swayarn jaa /
samudraartha yaa soochayapaavakaasta aap devi iha mamavantu //'
(Rig-Veda, VII 49.2)
The nature of water described in the ancient Indian scripture Rig-Veda translates as:
'The waters which are from heaven
and which flow after being dug,
and even those that spring by themselves,
the bright pure waters which lead to the sea,
may those divine waters protect me here'.
Spiritual veneration for water was absolute in the ancient societies, but it was always linked with great creativity for harnessing water. King Menes of Egypt (3 B.C.) diverted the River Nile with a 15m dam to establish Memphis, his capital city. Around that time the Egyptians had innovated 'Nilometers' to measure discharge of the Nile to divert excess water for agriculture. Around 1760 B.C. Hamnrnuarbi set in place the earliest known human laws for regulation, distribution and maintenance of irrigation structures. Another 60 years later in 1700 B.C. a dug-well in Egypt had reached to a depth of 100m to tap the water table and water tunnels were being used in Palestine and Syria to divert water from natural springs to towns.
Our ancestors were apt with the art and science of water. Since respecting the Nature was inborn, water was considered divine. Rig-Veda is full of 'shlokas' in praise of Water, Sun and Air, the three essentials of our environment.
The connection between the origin of the earth and water is mentioned both in the ancient scriptures and modern science. Rig-Veda, (X.129.3) says the earth was originally all water without light. Expert on geo-tectonics, Deming in one of his papers published in 2004 claims that Plate Tectonics started on the earth 2.5 billion years ago. Prior to this during the first two billion years the nature of the Earth's crust is not known, evidences suggest formation of continental crust through hydrolysis of primordial crust. The process must have required huge quantities of water and that probably came from extra-terrestrial accretion!
The physico-chemical properties of water are such that it is a universal solvent. It is this property which makes water the major carver of the landscape of our earth. The landscape carved by water action is unique and distinctive when viewed from the space.
The bi-polar structure of the water molecule which makes them adhere to hydrophilic surfaces. Silica and silicates the major constituents of the earth's crust have hydrophilic surfaces and water easily adheres to them and travels long distances through capillary action. Similarly this property of water keeps the plants growing, because it can travel through the capillaries of xylem, the 'food pipes' of plants and climb great heights against gravity to keep the plant green.
While the solvent property of water has many uses, it has a nuisance value too. In the course of its slow travel through the grains of sand in the sub-surface naturally occurring elements like arsenic and fluoride also get dissolved in water. Because of this, millions of people in West Bengal, Bangladesh and Nepal are facing the acute problem of arsenic and fluoride toxicity via drinking water from the tube wells. These are some attributes of water which are useful for water harvesting and the information comes handy while attempting to 'catch the water'.
In contemporary world, water is a matter of discussion and concern amongst the scientists, sociologists and economists alike. How judiciously we can utilize the water available without political and territorial attrition between water deficient and surplus countries is a major concern.
Before plunging in to art of harvesting it is useful to have a peep into the 'water budget' of our Planet. Out of a total volume of 1.36 x 109 x km3 major part (97.3%) of water in the hydrosphere is locked up as sea water, and another 2.1% in ice caps and glaciers. Marine organisms have the capability to survive in the saline waters of the sea, but others are not so fortunate. Freezing Glaciers have little fauna on them.
Fresh water essential for the survival of animal or plant life on the Planet is only 0.6% of the total water inventory.
Fresh water in lakes, rivers and atmosphere is less than 0.05% of total water available on the Earth. Atmosphere alone holds about 13,000 km3 or 0.001% of the Planet's water. A bulk of this freshwater inventory occurs as groundwater.
Statistics makes things sound simple. It is the miniscule percentage of water inventory, the groundwater which needs to be recharged in the water deficit areas. However, in reality the problem becomes gargantuan in terms of widespread water deficit and thickly populated areas.
It is amply clear that recharge of groundwater is from surface water and rains. Surface water hurtles down through streams and rivers and tries to reach its final destination, the sea. When the surface runoff is interrupted either due to natural or anthropogenic reasons impounded water forms lakes. In case of closed inland basins streams end up terminating in seasonal lakes. As water continues to flow in the stream a kind of natural balance is achieved. The balance is such that a certain quantity of stream water goes down to the sea and some quantity percolates to sub-surface to recharge the groundwater. A drainage network in a watershed thus established over the centuries provides the most efficient way of recharge of groundwater. However, the moment this arrangement of the nature is disturbed the natural forces start acting towards asserting a new equilibrium. Recharge of groundwater gets adversely affected in such situations. Water managers have to understand that a river is fed by several watersheds through streams originating in them. Human interference has to be checked/regulated in the watersheds to obtain optimum efficiency of the streams.
While attempting to harvest water certain basic facts must be borne in mind. The physical properties of water have already been explained. Water tries to travel through the pore spaces of unconsolidated or rather say 'soft rocks' like sand. Therefore if a pond is required at a place where a layer of sand exists immediately underneath the top soil, the scheme will not work. Water will travel down to depths. Thus a pond in making should have either a layer of clay at the top or artificial means of making the top surface impervious should be adopted. In hard rock areas artificial recharge of subsurface water is quite dicey. Before spending money on such a scheme even on a very small scale it is worth seeking expert advice. Probably the house owner may end up diverting all the harvested rainwater to the unknown abyss of the subsurface!
Watch out for more on potential of water harvesting in India in the next issue.