Thursday, August 25, 2005

Water is precious. Save it

Preserve and Save Water.

Catching running rainwater from various sources can help us capitalize on a vast water resource and solve water woes

What is rainwater harvesting?

Rainwater harvesting is a system by which rain is caught from all kinds of surfaces such as rooftops, gardens, roads, pavements, etc, and is purified and re-used for daily purposes. It can be used to perform two basic functions:

a) Recharging groundwater sources for later use;

b) Storing rainwater for immediate use and consumption.

Why do we need it?

With groundwater levels reaching dangerous lows it has become imperative for citizens to look for alternative sources of water, or the situation will grow from bad to worse very soon. This system has been operational in the developed countries for over a decade and has successfully managed water conservation. By catching running rainwater from various sources we can capitalise on a vast water resource and generate hundreds and thousands of litres of water every season that can help solve water woes. For example, a water tanker that brings water to your homes from unknown sources and unclear sanitation standards cost about Rs 1,000 to Rs 2,500 for about 10,000 litres of water. The RWH system gives you the same quality of water that you put into it without any extra cost.

What are the conditions that impact the structure of the apparatus?

The harvesting system depends on the following factors:

Amount of annual rainfall in the given area.

At an average, all areas where the groundwater level is more than 8 metres below the surface, groundwater recharging mechanism is advised to ensure that the water table is maintained for later use. Whereas those areas where the table averages between two and eight metres can go in for the storing device for cleaning and storing the water for use.

Demand for water generated.

The demand for water along with the available catchment area determines the size of the storage facility that is used. In building complexes and residential colonies, residents in the same building pool money and benefit from the water that is saved on their common rooftops, thus forming an economical and easy maintenance harvesting system. The materials and cost incurred during the whole installation and maintenance procedure. If the residence is in a condominium complex or a bungalow 75 to 80 percent of the RWH system is already in place and only the plumbing needs to be reoriented and the whole RWH mechanism is attached to the storm drain network that has already been established.

This mechanism will bring rainwater down using closed PVC pipes directed towards a sump (pit) and a simple three-part filtration unit consisting of sand, brick jelly and broken bricks.

Where sumps are unavailable old wells can be cleaned and used or new baby wells (2ft/l6ft diameter) can be constructed based on soil structure. For storing water for immediate use, the pipes bring down the water passing through a very small filtration valve containing wire mesh, small pebbles, etc, leading into large storage Sintex tanks placed at convenient locations for frequent usage. The water is then treated with chlorine tablets or boiled for drinking purposes.

Depending on the kind of model in your household and the terrain, the average cost of setting up an RWH system varies between Rs 2,000 to Rs 20,000. How does one ensure maintenance and quality standards? Since groundwater is replenished, care must be taken that leaking sewage pipes do not contaminate the recharge pit, etc, the filtration plant if cleaned frequently removes foreign matter, giving you safe usable water from your rooftop. The system should be cleaned twice a year preferably before and after the monsoon and does not cost much.

The Delhi government has assured to provide experienced staff for the annual cleaning and maintenance of storm water drains, etc, for all complexes that have taken the RWH initiative.

THERE ARE about 73 rain water harvesting (RWH) projects that have been set up in and around Delhi, for about four to five years now yielding tremendous results. A number of case studies prove its success.

"The Panchsheel Park Residents Association in New Delhi invested about Rs 8 lakh for the installation of an RWH system over 95 acres, and the average cost per household was only Rs 500. And today, the water table of the area has maintained itself for the 4th consecutive year where all other parts of south Delhi face severe water deficiency" — Salahuddin, Centre for Science and Environment

"We always believed a school to be an institution that sets examples and influences society in the most positive ways. This is why when the whole of Delhi was facing massive water shortages around 1999, our school set up the RHW plant with the help of CSE and the Central Government Water Authority, and we were in fact one of the first institutions in New Delhi to do so. The amount of awareness and sensitivity it has generated amongst the students has been overwhelming and now the whole project is completely monitored by students" — Madhu Bhatnagar, Deputy Head of Sri Ram School, New Delhi

"The year 2002 had been stressful, with Delhiites reeling under a major water crisis. But we have been spared now. We are using water frugally, but there is enough for us to feel comfortable" — Kulbhushan Oberoi, Chairperson, Oberoi Education Society commented, for Mira Model Public School

"No one knew what rainwater harvesting was all about when we decided to take it up in our college. As the work began the students grew curious and wanted to know more about it. Now everyone wants to adopt it" — Aruna Ludra, lecturer, Janki Devi College for Women

"We have actually recorded a three-metre rise in the water table within one-and-a-half-years! This is very exciting" — Prof PS Srivastava, Dean, Faculty of Science, Jamia Hamdard University

With New Delhi receiving an average of about 611mm of rain annually, and a rain water harvesting potential of about 450 billion litres, this figure can take care of about 35 percent of Delhi's demand of 838 million gallon litres per day. Many such cases are available to illustrate the system's advantages.



This article by DIVASHRI SINHA appeared in Tehelka

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