Every life form's depends on Water. Nothing special after Industrial Revolution, the world was soaked in new attitude towards environment. New term "Industrial estates" bloomed around the continents, disregarding wastage treatments, pushing untreated wastes organic as well as inorganic into the virgin natural environment causing the contamination of fresh water. The contaminants are of numerous as the list goes infinite, and most of them are directly related to the discovery and invention of some materials or things. Our authorities never think about the nature, they only thought about the exploitation of natural resources and how that exploitation can be done for economic benefits. So they wrote Laws and induced new projects that helped the exploitation at the maximum opening door for extinction of species. Species includes trees, plants, animals and all other forms of life. Now earth contains only selective species and only few areas have been unexploited, but threat of exploitation. These exploitations has opened another door breaking the food chain, leading some species reproduced and spread all around, some went out of the game.
I have found few reasons behind decrease in water table (base is the geographical location of Kerala)
Over population including the sociological disorganization of family systems from group family system to individual family system.
Individual family systems evolved with a direct effect on barren and agricultural, and forest lands converting it into residential areas.
Migration of population to rural areas created disharmony, and conflict between beasts and man.
By converting acres of open land into residential areas, directly the earth is becoming a desert area latently because rain water is made flow into ocean more rapidly affecting the water table.
Commercialization and beautification has created immense effect on environment. More people has relied on interlock tiles around their homes, painting and use of various chemicals in beautification contaminated ground water, where all one lives. Interlock tiles, easy water flow and obstructed water from entering the soil. (Urban areas are one of the examples, just look keenly, where all water enters soil? I don't think much places are there!) it is necessary to introduce a law regarding beautification and space management in Urban, rural and forest areas!)
Urban and residential areas created massive felling of large woods, unbalancing the ongoing natural environment. People are safe keeping small trees and shrubs, because they fear a wind uprooting a huge tree, or how much a huge tree takes their space. (People forgotten to think that trees are for nature and not for his selfishness and many more species are dependent on it.)
Deforestation ( I don't think much of the forests are left in Kerala, even inside forest I have seen numerous jungle lodges, and that has changed the behavior of animals and forests. (Who want to classify forests areas? Tourism?), directly effecting water table.
Stagnation of water by building bunds and Dams. (I want to show River Nila or Bharatapuzha which is one of the longest flowing in Kerala is almost dead)
Invention of JCB which threatened the hills and mountains. Shifting of precious stones and mud's from hills and mountains effects the down flowing streams and its existence.
Rice and Wheat fields are water reservoirs, using of chemical fertilizers, conversion of fields into residential areas has created immense impact on environment. (even though restricted by law, nothing happens for conversion, I have seen more fields are disappearing for residential areas)
Expansion of Tourism areas has created more threat to water bodies. Tourism has transformed more and more water bodies into barren lands by creating resorts and flats which directly pushed many snakes and related species to extinction.
Educational system has failed to nourish the mind of young, not to contaminate the natural environment through human activities, but they studied again and again how to earn money out of it.
The term "Development" has been misused; and the term itself has been the forefront of Political and Business game.
Projects commissioned are mainly taken as status rather than what a particular locality needed disregarding environment. Majority of open lands and fertile lands are converted for business and other Industries pushing towards and extreme conflict between man and natural resources.
Most of the projects declared by the government and other authorities do not suit the particular locality. They also do not help the local people or other species. Projects are games of Politicians in the name of "Development".
More parks and naturally beautiful areas are transformed into concrete jungles. (I have seen interlock tiles are the only solution of beautification!)
Our Public Works Department and State Electricity board is seen responsible for felling huge and large trees around side the roads. (No pre-planning to protect those beautiful shade giving trees).
Environmentalists and related NGO's failed to act in time.
Yearly afforestation programmes during monsoon season by authorities and NGO's related are seen just mocking as they failed to check or protect the planted saplings growing. (yearly they plant different tree sapling on the same spot!)
Man's cunningness to choose best viable heuristics disregarding environment to achieve goals he needed. (many of the new roads are builded through forests because of this cunningness and heuristics)