The Initiative for Green Habitats represents a long term commitment towards providing solutions for the creation of Sustainable Built Environments. This blog attempts to provide an insight to our views, commentaries on our work, ideas that we are working on, and provoke thought where there are more questions than answers.

Thursday, January 12, 2012

Preach and Practise- A case for a more comprehensive addressal of a city's water needs through rainwater harvesting

Residential roofs account a maximum of 15% of a city's footprint. Private residential plots about 30%. While this a must tap in terms of rainwater harvesting, why neglect the remaining 70%?
Yes, all rain that falls on our roofs and sites in residential areas should be harvested by us. Similarly, shouldn't the govt agencies (and others) do the same with what falls on everything else? Privately owned residential land adds up to a maximum of about 30% at best, if you remove roads, parks, common amenities, waste lands, nallahs, lakes & tanks, industry and government owned land. (You will find govt. figures putting residential areas at about 43%, but this is the area that the zone occupies, which also includes internal roads, other functions, etc). For resource strained cities, the remainder beyond residential footprints is a great catchment that we simply cant neglect. It is commendable that the city's infrastructure agencies are encouraging it's citizens to participate (and share the burden) in harvesting rainwater. The idea is right.... that if we, en masse, harvest the rain we will greatly reduce our days without water and effectively the water man's burden. Having said that, it only makes sense that the govt agencies, that occupy (or are in charge of) the majority of these lands should lead by example. Not only does is set the right tone for others to follow, but also adds substantially in recharging the natural coffers.
Currently, our civic agencies treat rainwater like the plague, encouraged more to draining it away as quickly as possible. What little benefit we get currently is perhaps a result of their (and our) sloppiness.... clogged drains, illegally created structures, etc, creating check dams allowing some of this rain to percolate into the soil. But why cant we address both these issues of recharge and drainage simultaneously? Consider creating holding ponds (opposite to closing lake, tanks and valleys), and percolating channels (instead of concrete lined drains and canals) for a start.
Bangalore city's rainfall distribution. The current demand is close to the
rainfall potential on private residential  plots, but what about tomorrow?
Take a city like Bangalore, with about 1279 square km city spread (green belt and all included) and a healthy rainfall of about 1000 mm, that amounts to about 1 trillion litres of water that falls every year! The current need of water in this city is about 440 billion litres year. The city water infra authority supplies us about 328 billion litres per year and claim a shortage. Glaring isn't it? What is shocking though is that our city agencies do not tap for a single drop of all the rain that falls in their current supply. All of the water is brought to us from three external sources. Most of it from the cauvery, over a 100 km away, and nearly a 100 stories below at tremendous energy costs!! The calculation of water need according to the govt water infra agency is based on a figure of 140 litres per capita per day (the supply is stated to be about 120 lpcd).... but isn't that only a figure of domestic need? Even according to the agency's own admission, only about half this water supplied is used by residences. The rest is used by industry, commerce and so on. What this means is that the water per capita supplied per home is actually at about 60 litres per day!! So where do these homes get their remaining water? From the ground!
The truth is that in most of our cities and towns, a large percentage of the water need is met by drawing it from the ground. When this is not countered by adequate replenishment of these reservoirs through appropriate harvesting it leads to depletion of the ground water table. What compounds this is that water is used by industry, institutions and commerce too.... a lot of this not met by the civic agency's supply!

A city like Bangalore has the potential to host nearly twice its
current population if only it harvests the annual rains well
As a reaction to these alarming rates of ground water depletion in addition to the pressure to supply a burgeoning population, the civic agencies have resorted to directing its users to take up the cudgels on their behalf. As stated earlier, commendable move. But the stats dont stack up.... Roofs account for about 10 to 15% of a city's total land area, and from where I see it it is more beneficial to use this directly (after appropriate filtration), instead of recharging it, and then withdrawing it with greater energies spent, and needing much greater filtration. The average coverage of built to plots (in total across the city) is anywhere between 30 to 50%, and what rain falls on the un-built portion of these plots HAS to be put into the ground (again after responsibly filtering it). But what about the remaining 70% of land that is beyond private residential plots? Just this portion can mean about 700 billion litres of water per year.... more than twice our current demand. I am not even considering the areas beyond the metropolitan limits, which still are part of the catchments that can influence the city's ground water. Zone wise commercial and industrial areas occupy about 10%, and in Bangalore city, they have been directed to harvest water too. What is worth reckoning for a city like Bangalore is that the amount of rainfall that can potentially be harvested in the city limits can potentially help serve its burgeoning population.

We are back to what a city's administrative bodies can do. We need to look at a city as a very large community on a very large parcel of land. Where rain falls should become the responsibility of the group that   is in charge of that area. So, like when rain falls on private residences they have to harvest, similarly, if it falls on roads or parks it should become the responsibility of the municipality, or, when it falls on a govt institution's land they should be. Get the remaining land holders like the defence establishments, religious institutions and industry to do their bit. They are a part of a city's dynamic aren't they? The city water supply authority (in Bangalore) has taken some steps, like the  proposal for the rejuvenation of lakes to serve as alternative reservoirs, or the proposal to treat sewage and loop it back for consumption, to address the city's growing water need. However, we need a clear and comprehensive water plan, that can cover a wide spread harvesting / recharge plan, that lists out separate maintenance, appropriate treatment, public accounting and specific responsibilities of all groups concerned. We are all players in this community that we call a city, and we all need to do our bit to share the responsibility.

No comments:

Post a Comment