Too simple to bother

The concept of rain water harvesting is disarmingly simple. It is easy to install and easier to maintain. Yet, RWH has not caught on in the metro. Just as using helmets was once mandatory, RWH could also be -- provided policy makers chose to respond to the reality, says GOUTAM GHOSH in his concluding part.

IF WE, the people, chose to wake up, we could sort out many of our civic problems. But as you will agree, it is impossible to wake up a person who pretends to be asleep. In other words, people hate to stir unless they are aggrieved.

Reasons are aplenty why rainwater harvesting (RWH) has not caught on. First, those who can afford it have never had to survive on water from sources they would refuse to look at, leave alone touch. If there is a crunch, they can buy jerrycans of water for uses other than drinking and cooking.

Second, many families avoid using their well water that may be cleaner and sweeter than the Metrowater supply. That highrises continue to drain the groundwater is a matter of concern more to water resource scientists than to the rest. Even a decade ago, residential areas not far from the seashore enjoyed both fresh breeze and sweet groundwater, but today the saline water intrusion is so extensive that borewells yield only brackish water.

(A civil engineering textbook - "Ground water assessment, development and management", Chap. 8 - proves mathematically how the extraction of water from an aquifer leads to saline water intrusion. The tendency to sink deep borewells is a tactical error as the density difference between saline and fresh water creates a cone of interface. The deeper you go, the quicker you will reach the salt water section unless you are far from the sea. One option is to identify the salt and saline water depths at a particular distance from the sea, and then use a shallow pump to pull out fresh water and another deep borewell to pump out saline water in order to maintain the hydrostatic equilibrium. The RWH recharge pipes will add fresh water that will tend to push the saline water towards the sea, unless the hydrostatic equilibrium has been disturbed. In other words, recharging the aquifer improves the hydrostatic gradient in favour of fresh water. There is much more to this than such a simple solution, but that is beyond the scope of this essay.)

Third, there has never been a scarcity bad enough to rock the Government which has hedged against this possibility by importing water from neighbouring districts and laying lines to get it from a neighbouring State. Fourth, as a corollary to this knife-edged plenty, the Government has never felt the need to make RWH mandatory and to frame rules to impose punitive fines on violators.

Fifth, people seem to believe that recharge pits will only benefit their neighbours. There may be some truth in this "free rider hypothesis". People tend to think, "If I can benefit from someone else's investment, why should I chip in? Anyway, he has sunk in his funds" - a real life instance of the fable about a king who wanted a pondful of milk for his morning bath but found it brimming with water when he went for his dip.

This is where the policy makers can come in. It would not be politically suicidal to promulgate a rule that no building could draw wellwater unless there was a working RWH system installed within. This rule could be relaxed for the poor who have no resources to harvest rainwater, except collecting it in plastic pots. So slum areas could be spared but any brick house within a slum would be required to do RWH.

Last but not the least is the one-time expense. This could range from a few thousands to more than a lakh, depending on the perfection desired and the area to be covered.

The concept of RWH is disarmingly simple: direct the rainwater from the terrace and the ground level to a pit and thence to the well which most houses have (diagram 1). The water level rises if the soil is clayey or if there is a solid rock base; the water seeps down to recharge the groundwater if the soil is sandy, as in the Adyar-Thiruvanmiyur area.

The major expense is in installing the pipes and recharge pits. This can be minimised if the system is installed when the building is coming up.

Buildings, especially highrises, tend to pave the common area which aids the surface run-off. None favours stagnant water except children who try their hands at basic origami to create paper vessels which keel to one side. Real estate promoters could easily aid RWH if they laid tiles, with gaps in between, on the earth bed around the building for water to seep in (diagram 2 and 3). The rest of the surface run-off could be directed to a pipeline around the building and carry it to the recharge pit.

It is necessary for each house to have a speed-breaker-like hump near the gate so that water does not flow out on the streets. There could also be a gate-level RWH system to trap the rainwater flowing on the street.

The hesitation of real estate promoters as well as people who build or own sprawling houses in the city is baffling. Real estate promoters can pass on the expense to the buyers; other owners can survive this pinch for a guaranteed long run benefit.

As the diagrams show, the system is easy to install and easier to maintain, provided they are not just recharge pipes which cannot be cleaned. There is no way to prevent dust from flowing into and clogging such pipes over time. As each 2400 sq.ft. plot received 1,91,000 litres of rainwater this year, if 50 per cent of this recharged the ground aquifer, 95,500 litres could have been added to the stock. That would have been 65 per cent of the water that an average family of five uses each year. This year only 233 litres seeped into each plot of 2400 sq.ft. on an average.

There has been an effort by the Corporation of Chennai to harvest rainwater in public places. Some of the flyovers have pipes to carry rainwater to a pit which was stated to be a recharge pit. There are metal sieves along both edges to trap rainwater.

Though a large number of these sieves are clogged beyond redemption, what needs to be appreciated is, the civic body realises that rainwater falling on fly-overs need not be wasted. The funnel at the collection point below a fly-over seems impressive but hardly adds to the efficiency of the RWH system. A straight link to the recharge pit would waste no water. It was impossible to remove the slab covering the recharge pit.

A blessing in disguise, if you wish. Whether the water flows to the edge of the flyover surface sooner than flowing down depends on the relative curvature of the surface vis-a-vis the gradient of the fly-over. There is no means to direct the water reaching the two ends of a fly-over. Water traps should have been provided but as Rajesh Lakhani, Additional Commissioner, Corporation of Chennai said, "We have taken the first step and will provide for water traps at both ends of a fly-over over time. We also do RWH in a number of corporation school buildings and parks." The technical shortcomings matter, but what matters more is RWH is being implemented.

One needs to question the need for storm water drains as it contradicts the concept of RWH. A system to harvest rainwater cannot co-exist with one to drain rainwater quickly into the sea. Instead of sinking recharge pits at the road level, the Government has spent lakhs on a system that is intended to prevent water stagnation on the road but wastes the rainwater in the bargain.

There has been an attempt by the city civic body to have recharge pipes in these storm water drains, but as Lakhani said, "Having such pits depends on where the sewer line is. The street level is raised over time, and it is possible that sewer water could mix with storm water if the two levels are close to one another. We would not like to harvest water that bears a load of sewage. The bacterial and other contaminants may not be removed by the natural filtration process and would reach the aquifer. That will be hazardous to health."

The system installed at a housing block in Adyar cost each resident family less than Rs. 1000. "The force of the rooftop rainwater filtered by the recharge pit was such that the inlet pipe to the well broke after sometime," the residents said. The jagged end of the pipe was a testimony to the awesome potential of RWH.

"The water quality has improved significantly, and we have water in the well everyday," the residents said. This should wake up the residents of water-starved Adyar-Thiruvanmiyur area.

Just as using helmets was once mandatory, RWH could also be - if the policy makers chose to respond to the reality. After all, only they can push the phlegmatic citizens to action.

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