Wasteful utilization of water, its contamination due to industrial effluents, its pumping up without recharging leading to drying up of aquifers, soil degradation and deforestation leading to run-offs, large scale evaporation due to the decreasing tree cover, have all led to a crisis of insurmountable proportions. But, the irony is that short-term, knee-jerk reactions in some pockets of Delhi are the only evidence of a small minority conveying their concerns. Is it not time that we wake-up to the stark reality rather than continuing with our complacent mind-set until the time when we are forced to stand in a queue for a few buckets of water.

In Delhi, the water table is declining at an alarming rate of 1 to 3 metres every year. The River Yamuna is a virtual drain from Wazirabad to Okhla. The present generation can never imagine that forty years back, the canals in NOIDA had plenty of water and people from Delhi used to come across the river on picnics and for swimming. The contaminated river is not only affecting the water table in a large area from where ground water is extracted but also the crops and vegetables grown in the region.

Recharging acquifers by harvesting rainwater

Delhi draws raw water from the Upper Ganga Canal and if its water is diverted for some other specific need, there is bound to be water-shortage. For example, from 15 to 30 April 2003, water from this canal has been closed at Haridwar for the Ardh Kumbh Mela. This has resulted in a huge shortfall of 20 million gallons per day at the treatment plant in East Delhi.

Due to the declining water table, tube wells are being sunk deeper and deeper. There is hardly any realization that drawing of water should be compensated by recharging the aquifers. The vast majority has no say in the matter and has taken a fatalistic view of acceptance of their fate. Those who can afford the money for such services, are sitting comfortably, digging-in every year and inserting additional sections of tubes to ensure a plentiful, twenty-four hours supply. They, however, are ignoring the fact that as depth increases so does the water salinity.

Media reports continue to surface with warnings from experts on rapid depletion of water resources. In Delhi, the requirement of treated water for drinking and domestic purposes is 830 mgd per day against the availability of 650 mgd of which 40% is lost in thefts and leakages.

Rainfall in northern India averages 800 to 900 mm per year. According to the 1991 census, the country had 9.49 million traditional wells and 8.22 million tube wells, the latter having increased enormously during the last decade. Dependence on river water has led to so much exploitation that many perennial rivers have no water left in the dry season. During one reasonably good monsoon, if the water is harvested, it can meet the demand for the entire year. By 2025, India will need 31 million hectare metres (mhm) of water for domestic purposes.

As a long-term sustainable option, rain water harvesting remains the only solution for water augmentation. It is the process of collecting and storing rain water and preventing its runoff, evaporation and seepage.

The topic is much discussed in meetings, seminars and conferences, with experts giving their views and media urging the public to gear up for action. It has to be understood in totality as to what is involved. The rain water on rooftops has to be collected through pipes that go down into the rainwater drain. This drain should not have any connection with the sewage system nor with the kitchen drain. The drain should lead into a number of underground tanks depending on the number of dwellings and the area to be harvested.

Mere underground tanks do not serve the purpose of recharging. Each tank should have a bore with a perforated tube going under the ground till about 20 to 30 ft above the water table. This would ensure the harvested water getting filtered as it seeps down and not contaminate the aquifer. The recharge structures should be away from the extraction tube wells. Existing but dried wells could serve the purpose of recharge tanks to reduce the need for drilling.

For any drilling to be carried out, permission of the Central Ground Water Board (CGWB) is obligatory. Although this is a genuine requirement to prevent unauthorized and excessive extraction, the following ground rules could be put in place.

The following is an illustrative theoretical calculation that highlights the enormous potential for rainwater harvesting:

In Delhi, average annual rainfall is 611 mm. A catchment area of 1475 sq.km. with the collection efficiency of 60% can yield 540735 million litres of water per annum.

Three most important components, which need to be evaluated for designing the rainwater harvesting structures, are:

A typical rainwater harvesting system comprises – a) catchment b) gutters c) pipes d) rainwater / storm water drains e) filter mechanism f) storage tanks or ground water recharge structures like pit, trench, tube well or combination of the above structures.

The cost depends on the volume of water to be harvested. The harvesting structure’s cost for a building (spread over 4 to 5 acres) that has 80 to 90 apartments, will be about Rs. 40,000. For a bigger plot that houses a bigger office complex or upto 150 apartments, the expense could be about Rs. 80,000. Almost equal components of this cost are – drilling expenses, brick work and filter mechanism.

Before giving the design of the proposed structures, one should look into the following essentials. Overlooking them may reduce the benefits: