27-09-2013, 04:49 PM
Rainwater Harvesting: Grab hold of Water Where it Falls!
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Abstract
Till about thirty years back, the areas around our homes and offices used to be unpaved and the rain
falling on these areas would percolate into the soil and remain there for being drawn through shallow
open wells. With the proliferation of flat complexes, not only have these areas been paved and
percolation of rainwater into the soil almost totally stopped, the quantity of water drawn from the soil
below has increased manifold. Consequently open wells and not - so - deep bore wells started drying up.
The reason is that no sincere attempt is made to replenish the ground water table with rainwater during
the monsoon. The Rainwater harvesting is the simple collection or storing of water through scientific
techniques from the areas where the rain falls. It involves utilization of rain water for the domestic or the
agricultural purpose. The method of rain water harvesting has been into practice since ancient times. It is
as far the best possible way to conserve water and awaken the society towards the importance of water.
The method is simple and cost effective too. It is especially beneficial in the areas, which faces the
scarcity of water.
People usually make complaints about the lack of water. During the monsoons lots of water goes waste
into the gutters. And this is when Rain water Harvesting proves to be the most effective way to conserve
water. We can collect the rain water into the tanks and prevent it from flowing into drains and being
wasted. It is practiced on the large scale in the metropolitan cities. Rain water harvesting comprises of
storage of water and water recharging through the technical process
Introduction
It was very difficult to imagine few decades before that you will require to buy drinking. The use
value of water was never undermined, but its about time that even its exchange value is given due
importance. Fresh water today is a scarce resource, and it is being felt the world over. More than 2000
million people would live under conditions of high water stress by the year 2050, according to the UNEP
(United Nations Environment Programme), which warns water could prove to be a limiting factor for
development in a number of regions in the world. About one-fifth of the world’s population lacks access to
safe drinking water and with the present consumption patterns; two out of every three persons on the
earth would live in water-stressed conditions by 2025. Around one-third of the world population now lives
in countries with moderate to high water stress—where water consumption is more than 10% of the
renewable fresh water supply, said the GEO (Global Environment Outlook) 2000, the UNEP’s millennium
report. Pollution and scarcity of water resources and climate change would be the major emerging issues
in the next century, said the report. These issues would be followed by problems of desertification and
deforestation, poor governance at the national and global levels, the loss of biodiversity, and population
growth, said the report - The Observer of Business and Politics, 12 October 1999.
Need for Water Harvesting
The scarcity of water is a well-known fact. In spite of higher average annual rainfall in India (1,170
mm, 46 inches) as compared to the global average (800 mm, 32 inches) it does not have sufficient water.
Most of the rain falling on the surface tends to flow away rapidly, leaving very little for the recharge of
groundwater. As a result, most parts of India experience lack of water even for domestic uses.
Surface water sources fail to meet the rising demands of water supply in urban areas, groundwater
reserves are being tapped and over-exploited resulting into decline in groundwater levels and
deterioration of groundwater quality. This precarious situation needs to be rectified by immediately
recharging the depleted aquifers.
Hence, the need for implementation of measures to ensure that rain falling over a region is tapped as fully
as possible through water harvesting, either by recharging it into the groundwater aquifers or storing it for
direct use.
Rooftop / Runoff Rainwater Harvesting for Artificial Recharge to Ground Water
Water harvesting is the deliberate collection and storage of rainwater that runs off on natural or
manmade catchment areas. Catchment includes rooftops, compounds, rocky surface or hill slopes or
artificially prepared impervious/ semi-pervious land surface. The amount of water harvested depends on
the frequency and intensity of rainfall, catchment characteristics, water demands and how much runoff
occurs and how quickly or how easy it is for the water to infiltrate through the subsoil and percolate down
to recharge the aquifers. Moreover, in urban areas, adequate space for surface storage is not available,
water levels are deep enough to accommodate additional rainwater to recharge the aquifers, rooftop and
runoff rainwater harvesting is ideal solution to solve the water supply problems.
ADVANTAGES OF RAINWATER HARVESTING
1. To meet the ever increasing demand for water. Water harvesting to recharge the groundwater
enhances the availability of groundwater at specific place and time and thus assures a continuous and
reliable access to groundwater.
2. To reduce the runoff which chokes storm drains and to avoid flooding of roads.
3. To reduce groundwater pollution and to improve the quality of groundwater through dilution when
recharged to groundwater thereby providing high quality water, soft and low in minerals.
Design Considerations
Three most important components, which need to be evaluated for designing the rainwater harvesting
structure, are:
1. Hydrogeology of the area including nature and extent of aquifer, soil cover, topography, depth to water
levels and chemical quality of ground water
2. Area contributing for runoff i.e. how much area and land use pattern, whether industrial, residential or
green belts and general built up pattern of the area
3. Hydro-meteorological characters like rainfall duration, general pattern and intensity of rainfall.
Cost Analysis
1. Cost of a Rainwater harvesting system designed as an integrated component of a new construction
project is generally low.
2. Designing a system onto an existing building is costlier because many of the shared costs (roof and
gutters) can be designed to optimise system.
3. In general, maximising storage capacity and minimising water use through conservation and reuse are
important rules to keep in mind.
4. With careful planning and design, the cost of a rainwater system can be reduced considerably.
Concluding Remarks
It is no denying that sustaining and recharging the groundwater along with judicious use of the limited
fresh water resources is the need of the hour. If sufficient measures are not taken up immediately, we will
face a crisis which will be detrimental to the very survival of mankind. Efficient management of water
resources and education about judicious utilization of water resources along with measures of
harnessing, recharging and maintaining the quality of water and water bodies has to be taken up on war
footing.
One of the most logical steps towards this goal would be acknowledging the importance of rainwater
harvesting. This should not only encompass rooftop rainwater harvesting but also storm water harvesting
systems. Storm water harvesting is yet to be acknowledged as a better alternative over rooftop water
harvesting. One of the major hurdles in storm water harvesting is the poor state of storm water drain
systems in India. A planned approach is hence needed in order to fully utilise the potential of rainwater to
adequately meet our water requirements. Hence, an equal and positive thrust is needed in developing
and encouraging both the types of water harvesting systems. We have to catch water in every possible
way and every possible place it falls.