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The Water Workshop for Apartment Communities - BIOME @ Redwood Apts

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Venue: SJR Redwoods,

Off Haralur Road,

Off Sarjapur Road,

(Turn right before Spring Fields Apartment)



To day 06-Dec-2009 (Sunday) there was this Interesting Seminar at SJR RedWoods, Harlur Road, Off Sarjapura Road, Bangalore at 9AM. It went on till 1:30PM. [ ] is interesting Web-based software for Management, Accounting and Communication in Apartment Complexes.


The seminar turned out to be a professionally organized workshop. The discussions were moderated by Mr. Subramanian Vincent Managing Director and Editor of OOrvani Media Pvt Ltd. Who are the editors for “Citizen Matters Bangalore”  publication. The following were the main speakers and active participants:- 

1.      Avinash Krishnamurthy Executive Director, BIOME

2.      Shubha Ramachndran, Water Sustainability Consultant

3.      S Narahari, Assistant Executive Engineer, BWSSB

4.      Prabhu Citizen Matters

6.      Karan Journalist BIOME

7.      Nate Stells Consultant, Biome

8.      Ranganath MD, Ion Exchange, India

9.      Sunil Jayawant

10.  Anil Lobo

11.  Bhardwaj

12.  and many more 

The main agenda for the workshop was to 

1.      Action points for conservation of water resource

2.      Bigger Water Picture

3.      Waste water Management

4.      Mandatory Clauses of BWSSB Regulations

5.      RWH Example case studies 

Round table discussions were planned but did not consummate fully as the discussions and queries for each of the speaker became difficult to manage. In fact the snacks and tea was served while the workshop was in progress. As I understand this may not be the last workshop for our city of Bangalore from BIOME. 

S Narahari AEE, BWSSB was the first to speak He has 28 years experience at BWSSB. BWSSB has a mandate on the core area of potable water supply to the city of Bangalore together with safe disposal of Sewerage water. BBMP is characterized by 

1.      Area                 : 1300 Sq KM

2.      CMCs               : 1275

3.      CDP                  :  594

4.      Core Area        : 229 Sq KM

5.      Periferal Area   : 365 Sq KM 

The main source of water to day is river Cauvery and 54 MLD of Tippagondana Halli reservoir.  Total Drinking water supplied by BWSSB is 959 MLD as on today. The cauveri Water is pumped form a distance of 100 KM over a head of 500 Meters. This supply is at a cost of 2.8 million Rs per month of electric power, with corresponding Global Warming. 

The Demand as of now is 1125 MLD.  There are plans to increase the supply from the current levels to 1125 MLD by 2012 when the Cauvery water will reach the maximum available limit. This is the reason for the current policy of RWH. 

BWSSB has these as the proposed solutions 

1.      Recycle water

2.      Dual Piping for

a.      Drinking

b.      Sanitation

3.      RWH

4.      Restoration of Lakes

5.      Etc 

BWSSB currently has 

1.      5638 Km of Pipe lines

2.      46 Chlorination Plants

3.      1920 Minor STPs

4.      1950 Major STPs 

It also has Voice recording complaint phones and 74 Kiosks. Mr. Narahari also pointed out that People in CMC areas have to start paying charges for future DW supply plans of BWSSB 

1.      0-600 Sft          Rs 4000/-

2.      600-1200 ft      Rs 8000/-

3.      1200-2400       Rs 16000/-

4.      >2400              Rs 24000/-

Mr. Avinash Comlimented BWSSB as the best board of its kind in India. He reminded the Audience about “Water Adalat” was there for any complaints, and not the workshop, as some tendency to complain / rant was exhibited by us including me!! 

Karan Journalist, Biome 

He felt that Bangalore is blessed with Rain water which is double the present requirement. Bangalore has an average Rainfall of about 970mm per year. Hence RWH has the relevance. 

Nate Stells, Biome 

He talked about case studies in the context of

1.      small, medium large size Apartments

2.      Strategies adapted

3.      Hydrological behavior etc. 

Examples were of 

1.      Jyoti Medows, CV Raman Nagar

2.      Tata Sherwood Apts

3.      Prakash Castle, RT Nagar 

Avinash Krishnamurthy, Executive Director, BIOME 

He started of with a video of a bore well, taken by a water proof camera mounted on probe which can be inserted into a bore well of any diameter. There must be some name to such a device I wish. The video delivery was fine tunable to freeze at any point of interest. We could see a very clear picture of the water from wall fissures appearing at various depths. There was an adjoining sketch to explain what and why of whatever was seen by the audience. Mr. Avinash must be having a true scientific and analytic mind. 

The most important point driven home by him was the single point of the benefits of ground water charging. Summarising his talk:- 

1.      Demand management

2.      Water literate / Responsible

3.      Engagement with communities

4.      Water Tarrif

5.      Gradations

6.      True Ecological water usage

7.      Defects of Gray water

8.      many more 

Mr. Ranganathan SS Consultant Total Water Management  MD Ion Excahnge, India 

He said that, being in the thick of water treatment, it was appalling to see very reputed builders in Bangalore are happly taking gullible Bangaloreans for a ride as far as STPs are concerned. STPs work on the principle of michrobic oxidation accelerated by oxygenting the sewage mixed with water sludge. It should be done at an open Corner of an Apartment complex, definitely not in the Basement of an Apartment.  Unfortunately BWSSB has failed to put any regulation on this critical issue. 

As Apartment Builders have no commitment to deliver a best deal to the customers in all respects whether apparent or not, they tend to cut corners. Consumers need to be educated by the city Fathers / authorities. The present seminar is a drop in the ocean. 

Mr. Ranganath felt thar sewage Contamination is on the increase alarmingly. 

Jayawant and Anjl Lobo 

·          Self Education

·          Sense of Community

·          Honesty is the best policy

·          ROI only to some extent

·          Have functional STPs

·          Water from STP not insignificant

·          RWH alleviates flooding

·          Low TDS [Total Dissolved solids] water 

·          Open Area to Roof area an impotent ratio for RWH

·          20’ feet depth of well for recharging in Bangalore

·          And more

After the workshop we adjourned to see what Shubha Ramachndran, Water Sustainability Consultant, Biome has done at Redwood apts. We got fairly good idea of what is roof top RWH and its economics. 



RKCHARI's picture

SJR RedWoods Apartment Meet

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Dear PSA,

In your characteristic fashion, you have given us an excellent report of the proceedings this morning at the RedWoods Apartment complex, Sarjapur Road. I would have liked to come, but urgent personal work kept me from joining this important meeting.

Reading through your report, I get the feeling everyone talked about the need for better and more efficient water manaqgement. But  no one seems to have spoken about the solutions available, except for Mr. Ranganath of Ion Exchange, who spoke about STPs.

I presume it was taken for granted that all apartment owners must install an RWH system as it has become mandatory. I wish someone had spoken about availability of agencies which actually install the units. I believe there really is none that is locally available. Most RWH Agencies tell you how to harvest water from rainfall, but none actually offer to do it for you!

Try asking the RWH helpline for actual help in harvesting rainwater and they go into a long harangue about various "simple" methods to do it, but no guideline on whom to contact and who would actually carry it out / have it installed in one's home.

Meanwhile, for Residents' Association of apartment owners, it would be heartening to know that HDFC Bank has taken a policy decision to extend loans to cover cost of installing community RWH Systems in highrise buildings, if Registered Residents' Associations would approach them with a formal proposal from any supplier of the entire system - from start to finish. HDFC can be paid back over any length of time that the Association feels comfortable paying back in.

There is a small interest amount charged by HDFC for such loans which my Company has decided to absorb completely, in the interest of promoting an important resource re-use for community welfare. It is all very transparent and there is no attempt to load the interest amount on to the product price or installation cost.

In the New Year (January 2010 onwards) my Company has decided to stock sufficient quantities of our products here in Bangalore imported in container loads so that anyone who wants to install a RWH unit would be able to do so by making just one phone call! We would arrange everything - from estimation, supply, installation to getting the bank loan sanctioned etc - literally a one-stop-shop which is truly hassel free!!

I hope this comment will not be construed as a publicity gimmick for promoting my Company and its products and services. I have deliberately left out name of Company and contact details as I want my present comment to be only viewed by all Praja members as  merely an attempt to share important information - not promote our Company. 






sanjayv's picture

Nice report

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 Nice report PSA sir.  There are couple of numbers that may have been misquoted, but you conveyed an overall message and most of the information.

@Chari sir:  BIOME is a for profit company started by the folks at the Non Profit Rainwater Club which installs RWH systems.  So this was a fairly practical series of discussions.  However, the information that you provided about the HDFC loans as well as your company's plans are nice to know.  Good luck.

psaram42's picture

May be it was deliberate

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@ Mr. Chari,

 You are right. That is exactly why the agenda was set by Biome as:-

1.      Action points for conservation of water resource

2.      Bigger Water Picture

3.      Waste water Management

4.      Mandatory Clauses of BWSSB Regulations

5.      RWH Example case studies 

If you had noticed, it was not intended to promote any company products and services, as such. The examples shown as implemented at Redwood Apts were by a company which was known to all. Hence there was no need to mention it specifically.

psaram42's picture

Some Pictures of the workshop

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 Picture-1 Mr. S Narahari AEE BWSSB




















Picture-2 Avinash Krishnamurthy  (sitting) and Karan Biome




















Picture-3 Subramanian Vincent OOrvani Media Pvt Ltd / Citizen Matters edit the moderator of the workshop.


Picture-4 Workshop Participents visiting the Roof Top RWH example at Red wood Apts 



psaram42's picture

There is a good ROI for RWH.

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 The problem here is that the roof top of the apartment itself is not available for RWH due to the penthouses occupying the roof. Hence they have used the club house roof top for the RWH. This RWH supplements the drinking water being supplied by Tankers, on a daily basis. 

 SJR Redwood has a huge RCC water tank of may be of 1 lack liters capacity I am not sure. This tank has been partitioned into 2 segments one for Tanker supply and the other for Club house roof top RWH water. Here the Piping from the club house to the actual location of the ground level Sump required a long pipe line adding to the investment cost. 

The second point is due to the area ratio of Roof Top to total area of the plot, there may be much more Rain water available than what is exploited right now. The golden rule is each person in SJR Redwood needs about x sft RWH area = factor x the drinking water allowance per person. 

Remember that “There is a good ROI for RWH.”

RKCHARI's picture

An Observation

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Dear PSA,

From the photographs of Redwood apartments it looks as it the penthouses have sloping roofs. Why cant water that falls on these sloping roofs also be collected through installation og gutters / mesh and downspout etc? If Penthouses have open terrace or roof gaden area, all the better. Water can still be harvested.

As you said it is apparent that only a small percentage of rain that falls on the entire plot is harvested. Anyway something better than nothing.




srkulhalli's picture

Give me the maths

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All talk, no maths !!

Can you tell how much rain water is harvested on an annual basis, and what percentage of it is of the total water used, for ANY case study above ? 


sanjayv's picture


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You can access some of the Math here for one of the case studies.

RKCHARI's picture

How "clean" Is My Valley?

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Sanjay Garu,

I bet you have read "How Green Is My Valley". On seeing the photos of installation through the link provided by you, I would like to ask one simple question: How "clean" is the source from which water for primary or secondary use is drawn?

Are Bengalurians interested in "naam-ka-vaste" RWH systems or are seriously considering water supplied through the RWH system as the main source of  this vital input?

Do the photographs showing sump and pit inspire confidence? In the 21st Century, are we not entitled to water being stored and supplied through crystal clear and 100% clean recepticals? Is it literally a pipe dream? (pun intended).

Think on these things!



sanjayv's picture

no idea

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 Dear Chari sir,

  I have no idea. Suhas wanted the Math.  I provided what I could find.  From the link, that may or may not be the final product... it could be a photo taken during construction.  Most of us use sumps like that to store water in Bangalore. Whether that is a good or bad method, I do not have the expertise to answer at this point.

psaram42's picture


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 @ Chari 

The reference provided by Dr. Sanjay gives the info about RWH economics in general. I think what Mr. Suhas had in mind for asking for “some numbers” has been to work out the economics of water in our city of Bangalore. The workshop at SJR Redwood did address this issue and much more in good measure. 

The mandatory clause introduced by the govt of Karnataka for the city boils down to 

  1. Harvesting for meeting pure water requirement of residents
  2. Ground water charging 

If we analyze the issue impartially the govt action has not come a day earlier / later than necessary. There has been no alternative choice. Sir M Vishweshwaraiah was a hero at his time for having built KRS dam and rightly so. However a lot of water has flown since his time. Currently the scenario is the Knee jerk reaction of the citizens and the govt. Let me try to give a fundamental calming way of approach to the whole of water issue. 

The per capita requirement of we in Bangalore let us assume at x=150 liters per day. If it has to come by RWH, for an average rain in Bangalore 0f 970mm in a year, the per person area can be calculated and hence the max density of population that can be allowed for the city of Bangalore. Taking the BBMP area we need to restrict the growth of the city population to that number. 

It is high time that we in Praja and other like minded organizations in Bangalore try and influence the policy of our governments be it BJP or any for all important issues like water and air.

Avinash Biome's picture

RWH for the City, Water Management, Economics and services

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Thank you for all the comments.  I hope to add value to this discussion and clarify the purpose of workshops which Mr Anantharam has briefly documented so well.

a) The total administrative area of Bangalore receives the equivalent of 3000 million litres a day of rainfall.  The current demand of Bangalore is pegged at around 1500 million litres a day.  It is estimated that around 40% of Bangalore's water is currently met by ground water.

b) Let us take a house of on a plot size 30 * 40 ft with 4 members consuming 135 litres per capita per day.  Its annual demand is 197100 liters.  Assuming 75% of the site is roof area this roof area receives around 80,000 litres a year which is 40% of the households needs in Bangalore with 970mm annual average rainfall. 

c) What it requires is an investment in storage, first call to rainwater during the rainy season.  If a strategy to use rainwater during the rainy season (Bangalore has two of these and a relatively well spread out rainfall pattern), the storages can be limited to the ones we construct at the start of house construction.  i.e. of the order of 6,000 - 10,000 litre sumps.  A well maintained terrace, good first rain separation and a good filter will ensure quality. 

d) So this means it can be retrofit to existing houses and planned upfront for new houses.  Retrofitting may be costlier than planning upfront.  If planned upfront the incremental costs are small.

e) In group housing contexts (eg: Apartments) because of lower roof catchment area to no people ratio the 40% number reduces but principles remain the same. In these context people need to come together which has its own process.  So the approach should be to do doable things (like in SJR Redwoods) demonstrate to the community and then take on higher investments incrementally to do more comprehensive RWH.

f) What cannot be stored can be recharged contributing to groundwater management - which has other components that were covered in the workshop which i shall not go into here.

g) If we see the above and consider that only 10 -15% of Bangalore's demand is non-domestic, the impact that RWH can have on overall demand is huge - therefore it is economical for the city.  The ROI of a specific RWH investment is a strong function of the water tariffs being paid by the location.  Remember our water is highly subsidised. At water tanker rates, Simple payback periods can be around 5 years for a specific installation that is retrofit.  That which is planned upfront the payback can be as quick as 1 to 2 years.

h) Coming to some points that Mr Chari has made - Of course as people start realising the power of RWH, there will be need for more and more service providers.  More and more integrated services will also be necessary and innovation and productisation will help the cause.  However all these processes have cost sensitivity too.  We are trying our best towards all these ends.

i) Yet for a service provider to be able to survive, there has to be a market.  The market right now is driven by scarcity of water/sense of water insecurity and of late the laws.  There are of course genuinely conerned and environmentally conscious people who form a part of the market.

Therefore we believe that the most critical part of the solutions to our water woes is a water literate citizenry.  The workshop's key purpose was this - communicate what water management is and what it means to us as a citizenry and for us as a city.  RWH is but one practice of good water management - it fits into a paradigm of good water management : that of demand management, groundwater management and waste water management. All of these need the citizen to be part of the solution not part of the problem.  It is this citizen that will then drive everything else - not only RWH markets but also ensure responsibility on the part of real estate developers that the process of real estate development is resposnible vis-a-vis land, water (or any other resource) through consumer action. 


Avinash Krishnamurthy










RKCHARI's picture

My Take

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Hi everyone,

I think any move to correlate population to availability of water and air would result in Praja being branded a reincarnation of Sanjay Gandhi himself!

We normally claim to calculate harvestable rain quantum as total catchment area multiplied by annual rainfall per square metre. So in a 40' X 30' plot it should be 112 sqm X 970 mm =108,640 litres and so on and so forth. Taking only roof area as one's catchment area may unnecessarily make one calculate lesser volume retention tanks. Moreover, the idea is to "save" as much rain as possible. Not only what is easily collectable. Then one might as well keep a few buckets out in the open and "harvest" rainfall in them, rather than going through the trouble of harvesting them from roof tops alone.

I also feel retro-fitting to connect a few downspout pipes leading to existing sumps is not a good idea. Firstly, sump water either from Cauvery supplies or filled with borewell supplies bought by the property owner in tanker loads are invariably ground water which contains many chemical contaminants. Mixing comparatively cleaner rainwater with sump water would contaminate rainwater per se and what we store for all our needs would be poor quality water.

RWH retentions tanks must invariably be separate tanks, preferably not made of brick and mortar as the concrete ones do tend to accumulate algae blooms if not cleaned regularly. If modular tanks which only store treated / filtered rainwater is an option that is now available, I think it is definitely worth promoting without reservation. If everyone is interested in providing good quality water rather than just any old water, some serious introspection should definitely form part of web initiatives like Praja forums.

To give another example, bad roads that we see today is because the earlier concept was to provide connectivity irrespective of its quality and long lasting features. Had we paid attention when roads were being built, today's roads would not be the sorry state it is in now. Same is the case with RWH. If the whole idea is to merely show the authorities that some slap-dash system is in place to comply with law we, the citizens will be the losers in the long run.

Creating awareness amongst citizenry is definitely a step in the right direction. But let us all ensure citizens are made aware of RWH's entire potential - not merely a convenient system.

I hope I have not tread on anyone's toes or ideas. I somehow felt Praja forum was meant to freely air one's views. Hence the long winded response!




silkboard's picture

Good report

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Cheap comment, just to say good report and discussion. Thanks Sanjay for pointing to biome website for some numbers. I am still learning the subject, so can't add any wise words here, but will certainly read all the maths you and others will point to.

sanjayv's picture

RWH, few more comments

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 Agreed that we should try to harvest as much rain water as possible, not just roof tops.  There may be practical constraints at different sites which we need to consider though.  After this workshop, I had a sit down with the office bearers of my apt community and we have decided to get our complex evaluated for feasibility.  I have been doing my own research in our complex over the past few days (something I've wanted to do for a while... this RWH stuff gave me a nice opening).  Without elaborating, the challenge has turned out to be more complex that what I had assumed initially.  In an existing building, you are really constrained by a lot of the hardware that is in place unless one is willing to  get the residents to all agree to pay for a lot of expensive retrofit in the space that is available.  People can quibble over costs... but having a mandatory law is making life easier. The second problem of course is the lack of information.  Drawings from builders has very sketchy details of a lot of the utility plumbing and such and one is forced to do a lot of surveying and pipe tracing.  (When I was in graduate school, the joke used to be that a Ph.D. from our group stood for a "High Degree in Plumbing".  Little did I realize...

Couple of comments though on Chari sirs post.

Firstly, sump water either from Cauvery supplies or filled with borewell supplies bought by the property owner in tanker loads are invariably ground water which contains many chemical contaminants. 

This gives an impression that Cauvery water is ground water full of contaminants.  Cauvery water is good quality water sourced from the river.  Yes, tanker water is a major scandal/ crime.


RWH retentions tanks must invariably be separate tanks, preferably not made of brick and mortar as the concrete ones do tend to accumulate algae blooms if not cleaned regularly.

Again agree, this could be an issue.  However, all our tanks (overhead, underground sumps) in banaglore are typically made of concrete.  What do we do?  Is there a major health hazard on our hands?

RKCHARI's picture

Response to SanjayV's post

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Dear Sanjayv,

I stand corrected about Cauvery water containing chemical contaminants. Technically, they are surface water and should not contain any contaminants.

However, I suspect BWSSB must be pumping the river water to central reservoirs where some chemicals are invariably added - not the least of which is Chlorine. Recent studies have pointed out that dosing of Chlorine too needs to be very carefully monitered. Excess Chlorine leads to long term effects on health. But no Chlorine is also not good because the reservoirs are open to contamination from elements and correct dosage is the answer. I am not sure whether BWSSB mixes any other chemicals. Some independent assessment done by citizens would help.

Tanker water is invariably full of contaminants.  In the gated complex I live, when our Association tested the tanker water being bought by us, out of 32 parameters, only one was within limits! We immediately changed the vendor, but I am not sure whether even that is safe.

Tanker water or Cauvery water if "treated" inside the home by Aquaguard or any of the newer filtration units does not eliminate bacteria. It only puts them to sleep for 8 hours and it is hoped that within that period the water gets ingested through the human body! No credence for bottles of water that we store in fridges during summer which invariably are stored way beyond the 8 hour limit!

The long and short of it is that we are all drinking extremely "suspect" water. I have my doubts about mineral water bottles too!

While I do not want to paint a bleak picture, clean drinking water is very much in shortage and the sooner we decide to drink boiled and cooled water the better.

Regarding installing retention tanks in places infested with underground sewage and water pipelines, electrical cables etc, there really is no solution unless one is able to get the detailed drawings from the Engineering Consultants who designed the PHE connections for the builder. Dont waste your time chasing the builder. Just get info on who were the Engineering Consultants / PHE Consultants and chase them for detailed drawings. Being professional, they are more likely to oblige.

I cant but help taking this opportunity to point out that modular retention tanks which can be fitted under any place - pathways, children's garden, car parking lots - which do not require any dedicated open area, are definetly a far superior option while considering placement of underground tanks for harvesting rain. It is also essential to "treat" rainwater with first flush diverters or roof gardens and then pass it through good quality mesh filtration units before saving harvested rainwater in tanks.

Regarding concrete overhead tanks already in existence, the only answer is for the Resident's Association to regularly clean and flush the tanks. Alternatively, you can install a few large sized Syntex Tanks (preferably the black ones) and connect the inlet and outlet from the point before it enters the conrete tanks to go through the syntex tanks and be collected there. Over a period of time the concrete tanks will become redundant. You can use it to store STP water for gardening purposes if your STP process is clean enough and does not have odour.

Hope I have answered your queries.




srkulhalli's picture

Some basic questions on RWH

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Thanks for the links and the discussions - I went throught the BIOME link.

1. The key question is how many days in a year can we survive on rain water alone and not depend on any other source. The answer from the website appears to be 1 month in a year, which is approx 7% - doesnt justify the hulla gulla that is created.

: The calculation used [total rain x total area] vs [daily consumption x 365] doesnt really hold good.  Just as an example, if all the rain were to fall on one day, that really wouldnt help us much. So it depends on three factors,

i) distribution of rainfall

ii)  the size of your sump tank and

iii) how long the water can stay in the sump and remain usable

Is there a way to put in the above parameters and answer the question I raised above. It must be fairly easy to create a model with the above.


2. The other aspect is if you cannot store it in a sump, recharge the ground water. I am not sure I understand this very well. Even if I didnt do anything, the water would eventually get into the ground - right ?. Else it would evaporate and form clouds and rain somewhere else and get into the ground again. There is nothing like your ground water and my groundwater, it does not respect any boundaries. So big picture - are we gaining anything at all ?




s_yajaman's picture

@ Suhas - rainfall pattern

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Here are rainfall statistics for Bangalore from the Hindu archives.  A bit more helpful than the 909 mm annual average.  The only guess was for Mar-May 2003 when I could not find data. 

Might help with questions (i) and (ii).  on (iii), someone more qualified will have to answer.  (i) and (ii) are essentially inventory management related and so I feel okay to hazard an answer.


Jan-Feb Mar-May Jun-Sep Oct-Dec Total
2000 0 132 675 333 1140
2001 0 386 467 198 1051
2002 0 189 358 217 764
2003 0 150 394 215 759
2004 0 260 699 179 1138
2005 0 249 673 675 1597
2006 0 289 297 92 678
2007 0 253 747 234 1234
2008 20 157 850 261 1288
2009 0 220 704   924
Average   229 586 267 1057

March to June is the time when the water crunch is in full swing in Bangalore.   And we get about 23 cm or 0.2m of water.  A 240 sqm site would be able to harvest 48m3 of water @ 100% efficiency or about 25m3 water at half that.  25000 l of water is 250 l of water a day availability (over the 3 months) - which is pretty good. 

What should we design the tank for?  If all this water fell on Mar 1 and nothing ever fell again we need a 25000 l tank.  But that would be unlikely.  It would also not fall very uniformly. 

We can plan for a peak rainfall of 10cm or about 12000 litres tank capacity.  This is a function of how much one wants to invest and how long the water is usable. 

On the groundwater bit.  In an ideal world it would not matter.  But in Bangalore, far too often it gets mixed with sewage and then goes down.  Therefore local recharging might be better.

Hope this helps.


Drive safe.  It is not just the car maker which can recall its product.

Ashika's picture

Thank you

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Thank you for the wonderful post on Water Workshop.

You can check the link here  for post workshop feedback and knowledge resource.

RKCHARI's picture

Lo & Behold!

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Dear SRK,

I am tempted to say "saari ram katha sun kar aap pooch rahen hain Sita kiske Baap hai"!

Irrespective of how many days in the year rain falls over any catchment area, every drop can be saved and reused.

Size of retention tank will depend on balancing water requirement per household with catchment area. NBC have indicated 135 to 150 litres per head per day. In a 40'X60' plot housing one house with 4 living beings, total harvestable water would be 222 SQM X 970 mm = 2,15,340 litres.

Now a family of 4 members would require 600 litre per day (4X150). Therefore, 100% rainwater harvested would cover 358 days.

Now do you see what the hulla ballu is about?




psaram42's picture

Potable / Drinking water

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 The drinking water requirement of a person (assumed at 2 liters per day) in Bangalore for an assumed rainfall of 9.7 liters per sq meter of area is met by 75.26 Sq meters (810 sft)of catchment area per person. The actual catchment area per person residing in a multi apartment building can be computed by dividing the building plot area (or roof top area in case of roof top RWH) by the number of people in the entire building. 

The BWSSB is currently thinking for going in for a dual piping system, for the entire city. The dual piping system is already in place for big buildings with many individual apartments . This was mentioned during the presentation in the workshop, by Mr. Narahari Assistant Executive Engineer. In dual piping system one is for drinking / potable water and the other for sanitation / non potable water, which can be recycled. 

The concept of dual piping system is useful in getting rid of present sewage water menace altogether, in the city. Each locality with a suitable upper limit of residents can have its sewage water treated locally and the water reused for sanitary purposes, like flushing etc. 

The cost of a RWH system, I believe, is mainly in providing the storage tank capacity. The importance of RWH is thus explicitly for meeting the drinking water requirement. Pure water not exposed to sunlight is for ever. Even to day people are solely dependent on well water in the country side for their potable water needs. Is there any expiry date for mineral water sold in bottles? I wonder.

thampan's picture


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RKC Sir,

the problem is that rainfall is not uniform in all days/months.

lemme give an example.

  1. Assume that rain falls only for the first 6 months and the remaining 6 months are dry. 
  2. Given this you need to store around 108 meter cube of water in a storage tank for the dry months ( assuming uniform usage of water throughout the year)
  3. this would mean a tank of 4.78 meters in all 3 dimensions
  4. Building such a tank is a costly affair ( be it modular or sump)
  5. In reality, this is more nuanced as bangalore would have around 9 months of rainfall with heavy rains on some days and light rain on other days.
  6. It is the size of the storage tank which is built which will determine the effective storage and thus what percentage of the rainfall can be used given the variable rainfall.


  1. A reasonable storage tank would be of the size of 3*2*3 = 18 metercube in my opinion. Given this storage capacity, you can check how much water can be saved and how much has to be let gone.
  2. If your assumption is that the storage tank can be of any size, then there is no issue at all :-) but resources are finite :-(


sanjayv's picture

How I view Rain Water Harvesting

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 As Chari sir pointed out, if you can harvest and store all the rain water falling on a 40x60 site  (theoretically) over the period of one year for an average year, the amount of water collected would be what is consumed by  a family of four consuming a reasonable 150 liters of water per person per day for a period of one year.  However, economics and storage capacity will limit what can be used directly.  Also for a residence with more persons or an apartment block, RWH will provide a smaller fraction of the water,

Another point to keep in mind is that RWH is not only to store in a tank and consume at a later point.  We also have the option of designing a ground water recharge solution.  Whenver rain comes down to earth, there are different places it could go.  A big fraction of that is run-off, which accounts for the water that eventually finds its way back to the ocean through water stream (rivers).  In highly built up urban areas, the run off is higher - one of the reasons why we see flooding when heavy rains happen.

Water supplied to Bangalore city by the BWSSB is substantially in deficit of the consumption. The remaining difference is made up by ground water (either from borewell or tanker).  Keeping that in mind, it is important for us to help recharge some of this rainwater back to the ground.  Upon recharge, there is no guarantee that you will directly see the benefit.  Quite possible that the recharged ground water goes to the neighbor.  However, the experience of other cities is that with widespread use of rain water harvesting, a general rise in ground water level is certainly observed.

So, to summarize ... the volume rain water that we get is sufficient to sustain a family of four comfortably on a 40x60 site.  Several practical challenges exist in harvesting all this water.  However, keeping in mind the precarious water situation for our city in the future, this volume of water is not trivial and can be used to augment our use as well as replenish precious ground water which is already a significant source of water in our city today.  This is one of those cases of where we have to look at what is good for the community at large rather than calculating individual ROI.  At any rate, RWH is only part of the solution.  We will need to continue to come up with innovative solutions of recycling, reuse and demand side management for the future.


psaram42's picture

The RWH perspective

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 Assuming a ball park value of about 970 mm average annual rain fall in Bangalore, the available water works out to be 97 liters per Square Meter catchment area for a whole year. With this as the starting data one can easily construct the following spread sheet application as a ready reckoner, for further fine tuning.  













Sq Ft















Sq Meters











Sq Mtr


   For a 60x40 site in Bangalore we have approximately about 600 liters of water per day. This water is the best naturally available pure potable water. 600 liters of equivalent mineral water would cost Rs 5000/-. The ROI on the RWH system would depend primarily on the cost of providing the storage tank and the required roof top plumbing. There is thus an enormous opportunity to innovate on the design of a cost effective water storage tank, along with the standardization of the plumbing part. 

The Rain water as per the above calculation does provide the necessary 135/150 liters per day per person including all daily requirements, for a family of 4. The figure of 150 liters per person per day includes bathing, washing, flushing, gardening needs, over and above that for drinking / cooking.

It is hoped that all the Architects, service providers and the RWH Industry in Bangalore / Karnatak would help providing a cost effective solution.


RKCHARI's picture

Wrong Calculation, I am afraid

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PSA Sir,

The average annual rainfall in Bangalore is 970 mm / sqm.

Therefore, if the catchment area is 222.97 sqm, the total harvestable rainfall is 970 X 222.97 = 2,16, 281  litres - not 21,628 litres.

This would obviously be sufficient to cover nearly 360 days at a daily consumption rate of 150 litres per head per day for a household of 4 persons.

In homes where they have more members - say 5 or 6, it would still cover 240 days. Actually, on an average no household consumes 150 litres per head per day. NBC calculation versus practical experience on a per head per day basis is as follows:

                                                           NBC                                          PRACTICAL TERMS

Drinking & Cooking                          5                                                         10

Flushing                                           45                                                          50

Bathing & Clothes Washing         25                                                         30

Utentsil washing                             20                                                          10

Gardening                                         25                                                          10

Miscellaneous                                 15                                                           -

TOTAL                                             135                                                         110    

Remember, these are per head figures. So if a household has 4 members, would a 40' X 60' plot require 100 litres daily to water their garden?

And how can you calculate on Miscellaneous quantity of 15 X 4 = 60 litres per day when the object is to make do with least wasteage?

Water, and that too clean drinking water is so essential and so precious, why do we junk all effective RWH systems providing clean drinking quality water as not being worth it unless it is COST EFFECTIVE? Can you put a cost to breathing fresh air? Should not the mindset change to get the most effective system in place rather than bother about how cost effective it is?

Just my two penny worth




sanjayv's picture


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PSA sir, your calculation should give you 970 liters per square meter and not 97 liters (per year).

Chari sir - plenty of people in Bangalore consume well above the 135/150 liter number.  This is backed up by data from the various RWA groups at the water harvesting workshops as well as data I have begun collecting in my own community.   In some places, a water consumption of even 500-600 liters per person per day was estimated!

One of the reasons for this situation is because in many communities, the water bill is part of a maintenance cost.  There is no penalty charged to individual home owners due to lack of individual metering. 


psaram42's picture

I stand corrected

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Now the figures look impressive. Coming to the cost effectiveness, I for one would go for that size of storage tank which would be cost effective for me. In essence it means that I will store only that much water which I need for Drinking, cooking and no more. The rest I will use for charging the ground water. Obviously no body would build a storage tank for all the 2, 16,000 liters, on a 60x40 plot housing 2 persons. 

If each house / apartment inclusive of their portion of the road, follows the above procedure in the core Bangalore city area, there need be no storm water drains. There can be impressive foot paths instead. 

In addition the present water piping can be used for only sanitary recycled water. The dual piping system planned perhaps may be superfluous.

RKCHARI's picture

Water Balancing

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Dear PSA Garu,

Obviously the tank capacity required by you for your home should not be more than 15,000 litres. This is arrived at taking into consideration the useage capacity and the actual rainfall pattern. In fact we have developed a software wherein if we input the length of the plot and usegage capacity, the tank capacity automatically shows up.

Sanjayv - Well that really is the main problem is it not? How can educated people living in metropolitan cities like Bangalore be literally "wasting" water using thousands of litre a day when in fact they should not use more than 150 litres per person?

Perhaps the answer lies in BWSSB going in for an austerily drive by educating people to save and conserve water, not waste it by just having a "couldn't care less" attitude. Instead of pictures of political leaders in half page newspaper ads extolling how they have inaugurated this water scheme or that, they should actually be crying from roof tops to save water - any which way.

Ensuring zero leakages in pipeline supplies either from BWSSB mains or within a gated complex where builders use substandard pipes which get rusted and develop large leaking holes is another big menace.

And finally, for as much of our non-potable requirement as possible (including bathing) we should use treated waste water. In fact in America there is sufficient studies to prove that in fact we can convert grey water into potable water. But if that is not feasible here, at least let us consciously try and wash our car, water our garden etc in treated grey water.

And yes, every citizen must pay for water that he consumes - whether from borewell, reimbursed through maintenance charges or for supplies from BWSSB mains. The shoe will only pinch when water becomes a paid commodity.

Jago Bangalore, Jago!





psaram42's picture

Some attempt to answers to the basic questions on RWH

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  1. On a 60’x40’ plot about 600 liters per day pure drinking water is available by way of RWH, which can meet the drinking water needs of 120 people @ 5 liters per day.
  2. Water if protected from sunlight can stay usable indefinitely long. Does your mineral water bottle carry any expiry date? Please check.
  3. In olden days people used to store “Ganga jal” in copper vessels for special occasion of putting it in the mouths of people on death bed.
  4. People use well water without treating in the country side. Does a well have an expiry date? It has to be hygienically maintained.
  5. Of course unused well water exposed to sun light will grow harmful algae. Such well has to be re commissioned before use.
  6. Recharging the ground water concept is very simple and is well understood.
    1. All the new apartments like Redwood and many shobha apartments are all getting bore well water. BWSSB Cauveri water has not reached there yet.
    2. The bore wells get their water from rain. [there is no other source water on this planet, except natural rain]
  7. BWSSB is already toying with the idea of dual piping system
    1. Potable
    2. Recycled Sanitary
  8. The size of the tank can be worked out on the basis of average rain distribution factor over a sufficiently long period. The optimum size of the tank can be determined fairly well by mathematical optimization techniques.
  9. However 7 above may not be important due to the ground water charging, which will keep the bore wells from not going dry. 

I am afraid there may be several loopholes in my attempt to answer the key questions. I have tried my bit. Please feel free to advice.

thampan's picture


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 have attempted some calculations and attached the excel sheet in

Around 75% of water need can be covered by using a 15K liter tank as per my calculations.

RKCHARI's picture

Many Thanks

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Dear Thampan Garu,

Your calculations are fine and can form a base for anyone who wants to start action to install an RWH system.

We also have devised a similar calculation sheet where we can also play around with weekly rainfall patterns to arrive at optimal tank size.

One point we all must remember is the fact that in all properly constructed underground storage tanks, the expense involved is only onetime. When calculating ROI how many of us realise that if you take a family's water requirement spread over say 10 years the investment becomes insignificant. One literally ends up having free water (whatever percentage it covers for the user) for the rest of one"s life.

Incidentally, I was recently informed that there are some water quality norms set by the Karnataka Pollution Control Board which makes it mandatory not to allow grey water (from kitchen, bath, and other waste water except from flush - which is considered to be black water) to be infiltrated to recharge ground water unless it is treated to potable quality level.

Is anyone aware of such a law?




n's picture

KSPCB - water treatment

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At RKCHARI: Some details on their "About Us" page and "Disposal .. distilleries" page. Couldn't find any online link to Water ... Act 1974 after a quick search. May be you can write an unbiased gyan on all water treatment, harvesting related issues (BWSSB gyan has already been started by sanjayv) ;-)

srkulhalli's picture

RWH not fully clear yet ...

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Thanks Sanjay, s-yajmann, Thampan we will come to it  shortly

RKC, as in the Ramayana, there is the story part, and then you read it again, and there is a deeper insight and the story is not exactly what it seems. Similarly, maybe you need to read the questions again !

1. Size of storage:   Thampan is on the spot with the XLS - very good -  lets continue on that post. [PSA - you mention mathematical optimisation techniques - sounds hi fi - can you suggest one that can work here]

2. How long water can stay good : Village Wells is a good analogy, though I dont see myself drinking water directly from a well. Is that recommended ? Mineral water is not appropriate comparison because it is vaccum sealed. Once you open the bottle - how long do you keep the water - I dont keep it for more than few days though there is no direct exposure to sunlight. I hope somebody can give a more scientific reasoning here. Of course, if it stays good forever, thats fantastic.

3. Why recharge ground water :  Still not convincing.  Most of it would find a way to the ground anyway and pretty close to the recharge point too. I have a decent sized garden in my house. Do I need to put in special recharge bore well or let the water find its course ? Whats the difference ? [Sanjay - why is the run off to rivers higher in urban areas ? if there is no river nearby ? ]


thampan's picture


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1. once you have an excel sheet which takes care of the daily/weekly rainfall pattern as well, you could use goal seek in excel to get the optimum size of the tank.

2. having drunk water from well for a good number of years, i can say that it is much better. The same cannot be generalized to water stored in the city tanks, but as long as there is constant inflow and outflow of water, the quality should not suffer.

3. in cities, most of the ground is impervious. Hence the rainwater flows to the SWD which carries it away from the city. If your garden has permeable soil and you can afford a small flood in your garden in case of heavy rain fall, you do not need a recharge borewell.

psaram42's picture

Mathematical Optimization Techniques

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 @ srkuhalli

These are rigorous techniques to get the optimum solution for a given problem. Simply put one needs to get 

1.       The objective function

2.       The Constraint functions and

3.       The design parameters.

If the objective function and the constraints are all linear then the problem is called Linear programming problem. In LPP the optimum lies on one of the vertices of the intersection of the multiple constraints. If any one of the above is nonlinear then the problem is a non linear programming problem. There is the third variety called stochastic programming problem when any of the parameters is probabilistic. 

The optimization problems are thus called programming problems when analytical solution does not exist. The optimum is obtained by a right royal search / study over the entire domain. The RWH is thus a stochastic programming problem. The best way to tackle is by the use of excel sheet, with average or most likely pattern of rain fall expected in a place. This is what Thampan has done so nicely. 

Ground water charging is important to conserve potable water for future use. For example Cauveri water is not enough for the current city population. By 2012 it is expected that there will be no extra water available from the river Cauveri. There fore it is but wise to charge the ground water table to an optimum level.

In the current RWH perspective, the objectives could be any of 

1.            Maximum benefit with minimum investment

2.            Capture of rain water for immediate use as well as for the  anticipated future dry season

3.            Tank should tend to be just dry at the start of full bloom rainy season.

4.            etc.


sanjayv's picture

First cut answers

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  Here are my first cut answers to your questions. Disclaimer: These answers are only "common sense" type of answers.  We'll need more research or need to find an expert for better answers.

2. How long water can stay good 

Water staying good depends on the quality of water.  If you have pure water (only H2O) in a closed container which is isolated from the outside... it will stay good forever.  The issue of water going bad comes from the quality or the container or the sealing.  There could be biological (microbial contamination) and those guys can multiply in the water and make it bad or living matter decaying can have harmful byproducts(high BOD - biological Oxygen Demand).  Alternatively, there could be chemicals in the water that reacts with the water... sometimes you can have photochemical reaction (light activated) with even a small concentration of contaminant Thirdly, the container may be bad.  Biological growth on the walls of the tank etc.

Rainwater itself, after some of the initial water flow which may contain some atmospheric contaminants, is quite good... it is condensed (distilled water).  The roof has to be clean or the water may pick up contaminants on the way to the storage tank.

3. Why recharge ground water :  Still not convincing.  Most of it would find a way to the ground anyway and pretty close to the recharge point too

Actually, the best I can figure out from reading, only a small fraction of rainwater finally gets to become true ground water. You have surface run off. In urban areas, with roads and storm water drains, water finds a real fast path to somewhere (in our case, the lakes of Bangalore. (As you know, B'lore lakes are artificial structures which are built in the natural drainage valleys leading to various rivers like the thenpennar, Vrishabhavati etc.).  Even some of the water that goes into the soil (like your garden) will flow laterally (subsurface runoff) and find a way to water bodies. Finally, quite a bit of water stored in the upper soil layers are used by trees and plants and lost back to the atmosphere.  Only a small fraction finds its way to the ground water table.  Hence the need for recharge wells that punches through the top layer of soil.

Basic funda is simple Suhas... assume that every surface that is exposed has a certain maximum recharge capacity.  Now consider that a huge area is built up (just like in Bangalore).  Isn't it fairly *logical* that recharge capacity will go down? Unless it is perfectly flat terrain, given sufficient rainfall, water tends to go to a flowing source.  Even a lake (which are also severely being encroached upon) has a set recharge capacity. Bangalore lakes are full of sewage... I would not want this clean rainwater to mix with all that sewage.  There are way too many arguments in favour of RWH Suhas.

RKCHARI's picture

Elementary,My Dear Watson!

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Dear Sanjayv,

You really have a knack of putting things in a crystal clear fashion. Your explanations to Suhas are perfect andcould not be expressed in more logical fashion.

I might add that if one has roof gardens, 99.99% of the atmospheric contaminant that comes down in the first flush of rain gets automatically filtered. Otherwise one must have what is known as First Flush Diverters which can be fixed at the outlet point of the roof water to ensure it takes care of the atmospheric contaminants, if any.

Even if it goes through a roof garden, water must be filtered at least at three points - outlet on roof, midway in downspout pipes and just before inlet pipe leading to storage tank. There are specilly padded micron filter which makes rainwater 100% pure and safe to drink. If rainwater is not being used for drinking / cooking, then such elaborate filtration systems need not be installed.

Another factor that must be borne in mind is that water stays fresh for ever if kept in black coloured retention tanks - way away from sunlight. Modular tanks which have clean riverbed sand compacted and surrounding the tank which is wrapped in geo-textile also helps in creating a capillary action which again helps in keeping water cool and crystal clear as well as fresh for eternity.

As you said, there are way too many plus points of the RWH system to wish it away!




srkulhalli's picture

Pretty good, one more clarification on storage

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Thanks Sanjay for some more clarity. What I get on ground water recharge is - in case of urban areas, there is more run off through storm water drain and others into rivers so it does not recharge the ground water as much as in case of an exposed terrain. Kind of convincing, but if somebody comes across more indepth info, please do post it.

Storage: OK, in case of an ideal container, it can last forever. But is there any data for the typical RCC sumps with a cement cover that we build. Its not perfectly sealed, plenty of air circulation - but its not exposed to sunlight. I think there can be microbial growth. How long would the water last in this - can anybody comment ?

Else looks like we should be all be purchasing RKC's tanks ! So when are you going to start selling them :)


RKCHARI's picture


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Dear SRK,

Concrete tanks even kept underground, do have algae bloom growh over a period of time. Algae blooms are really very poisonous. Only option is to clean the sump periodically. As is the case with concrete overhead tanks.

Now our modular / laticed tanks covered by geo-textile and wrapped in impermeable liner allowing for water to breathe and stay fresh is without doubt the best solution - am saying so unabashedly since I  know it is true and have no quams in saying the truth!

Atlantis tank modules will be available by end January 2010 as shipment will happen only after X'mas holidays are over on 18th Jan.

Would earnestly request everyone to try us out. We will even take it back if you are dissatisfied - without any questions asked! HDFC loan is begging to be taken for those who want it and as I said, we would absorb the interest on the loan!!

How much more easier can it get?




sanjayv's picture

Some links

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 Suhas, here are a few information sources

1. A general ground water primer - here.

2. A report on ground water recharge for the Upper Ganga Canal command region published by a scientist at the National Institute for Hydrology, Roorkee - here. There is a Chaturvedi formula in the report which gives a simplistic, first order idea.

3.For more specific information, we can contact the National Institute of Hydrology Regional Center in Belgaum. These guys are supposed to do studies specific to our part of the country.  See here.


srkulhalli's picture

An ecological nirvana - no waste water - is it feasible ?

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The other side of the story is to reduce water consumption as much as possible by recylcing and then cause minimal envioremental impact by having minimal or no disposal.

An ideal scenario would be if there is no sewage line at all and everything is reused/disposed at source. The advantages are too many - no sewer lines, you are alerted to various chemicals you use in your house and you are automatically driven to clean it up, and since your own ground water gets contaminated, you are automatically enviorementally conscious.

All envioremental issues come about because you dont face the results of your action directly, but it is shifted in geography (disposal is somewhere else) and in time .. comes and hits us in the future.

In this age of miniturisation, why cannot a treatment plant be reduced to work for a 60x40 site ? Is there anything outthere for recycle/dispose at source ?


psaram42's picture

It is feasible

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 An online dictionary says: 

Feasible = Capable of being accomplished or brought about; possible 

In fact in places where there is no community sewerage system you have to have individual solutions. In villages of India and perhaps in many developing countries like India there are private solutions for sewage disposal. Have we not heard about Septic Tanks? Earlier in Bangalore I have seen people having Septic tanks constructed in their sites when there was no public sewage pipe to connect to. The sewage was let into a covered pit. They had two such pits for alternate use. 

Now we have huge Sewage treatment plants several of them in the city of Bangalore. Again this is an optimization problem. You have thought about the solution at the lowest side. The highest would be one STP for entire Bangalore. However optimum would perhaps be in between.  The city designers have to work out the optimum size of a community which should have its own sewage plant. 

An ideal place to locate this optimum plant would be the community parks. The manure from sewage plants could be consumed in the park itself. I have been toying with this idea for some time now. Hence I was glad to see the above comment. 

psaram42's picture

Ground water is not your own

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@ Suhas 

Once you let your water in to the ground it is not yours. It finds its own way which is not under your control. About harmful chemicals one need not invent the wheel over and over again. Lot of gyan is available on the web perhaps? 

The real situation is people indulging in Industries which do produce harm full chemicals would like to dispose them somewhere else. My earlier blog entry refers. comment guidelines

Posting Guidelines apply for comments as well. No foul language, hate mongering or personal attacks. If criticizing third person or an authority, you must be fact based, as constructive as possible, and use gentle words. Avoid going off-topic no matter how nice your comment is. Moderators reserve the right to either edit or simply delete comments that don't meet these guidelines. If you are nice enough to realize you violated the guidelines, please save Moderators some time by editing and fixing yourself. Thanks!

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