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Inputs sought for a low-cost Rainwater Harvesting filter design

Respected Experts in this field,

Common problem areas in the RWH systems being the availability of filters and their costs. People though may be enthusiastic in implementing the RWH systems may be discouraged due to the fact about non availability of economical filters to suit recharge/reuse of rain water. I have heard some cases through my limited knowledge, where in general innocent public are short changed by the filter suppliers.

Here I have tried my own design of filter to recharge my exisiting well, please go through the same, suggest any improvements which might help people who are on a shoe string budget. Suggestions, development on this particular model or any new design which is very cost effective, build on own with available materials  and occupies less space would be useful for the public,


Thanking you in advance


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CommonMan's Filter-Ajith.doc1.15 MB


1. Dear Mr. Ajith, Greetings

Dear Mr. Ajith,
Greetings from KSCST and I appreciate your interest in innovative ideas for Rainwater Harvesting and water conservation. In fact the best filter for rainwater is a simple first flush valve and sand bed filter. Further for ground water recharge through pre cast cement ring wells in Bangalore do not require filter if the water is coming from roof tops. Rainwater from the down water pipes can be let in to the aggregate layer around the cement rings (not directly in to the well). Leaves and other debris remain on the surface and water reaches the well through gaps further down in the well.
With Best Regards,
A.R. Shivakumar
Principal Investigator - RWH
Karnataka State Council for Science and Technology
Indian Institute of Science

2. Response

Dear Ajith,

Really it is an innovative and cost effective filter designed. The only aspect is to have a first flush provision and the individual roof has to be clean enough.
With regards,

D. Chakraborty
Central Ground Water Authority (CGWA)
New Delhi

3. RWH Filter

Respected Mr. Shivakumar and Mr.D.Chakraborty,

Thank you for your comments, feel honored to receive comments from eminent personalities like you both,

I have also incorporated the first flush arrangement, i shall update the website at the earliest


Ajith P

Life is Simple, We make it Complicated.

4. On rainwater filters

Had done an article for The Hindu in May which may be of interest to you




5. Dear Ajith, Mr. Ajith is to

Dear Ajith,

Mr. Ajith is to be commended for striving to design an inexpensive user-friendly filter for rainwater harvesters. Since he has asked for views of others on his innovation, the following comments are offered:

For   assessing the   practicability of any rainwater filter, the following criteria need to be considered, as the target volume of water to be collected is quite high:

  • The collection area
  • The suspended solid content  of the feed water
  • The volume of water that it can filter before it needs maintenance such as removal of mud from the clogged filter
  • The rate of filtration (i.e. litres per minute)
  • User-friendliness i.e.  They should need minimum human intervention; time taken for the media replacement and skill needed for the replacement should be limited.
  • Cost of replacement of the filter media
  • Capital cost

In the filter designed by Mr. Ajith, items, 5, 6 and 7 are satisfied but in the absence of more precise information from him on the other criteria, my preliminary assessment is it may be suitable for a small terrace area in a place where the rainfall is gently spread and not heavy and inn short spurts.
However, based on my field experience, I would state that the filter area is very limited and the pores in the sponge will get clogged very quickly. If it is filtering large quantities (given that it is draining terrace rainwater into a well) without getting clogged, this could simply be because the terrace is more or less free of any mud and so the rainwater is practically free of any fine mud. Moreover, in apartment complexes, the volume of rainwater will be many times larger than that in Mr. Ajith’s house and there will be multiple terrace-pipes coming down and so installing filters at each down take point and maintaining them will not be convenient.
In my two –decade experience in RWH, I have not come across any filter yet that fulfils the criteria cited above. My solution for the problem of filtration in over 150 residential apt complexes in Chennai was to recommend sweeping the terrace clean of mud and leaves before the monsoons break. The problem of leaves is solved in most cases by just pruning the over-hanging branches of the trees that have grown higher than the terrace. Also, if the terrace water is to be drained into a shallow dug well or a sump, even if some mud comes along with the water into the sump or well, it will be only sterile mud and even this will settle at the bottom (just as the mud from the piped water supply settles at the bottom).It may also be pointed out that there is already a lot of mud at the bottom of the shallow well! Again, when this water is pumped into the over-head tank, there will be again settlement of mud at the bottom. Those who use this water for cooking can simply filter it through a piece of cloth, if necessary. We put an elbow  at the terminal point of the pipe inside the well so that the water does not fall down with momentum and create turbulence in the standing water column of the well ( particularly when the water level is low). The elbow directs the water on to the wall of the well which neutralizes the momentum and the water drains down smoothly along the wall of the well.
In the case of sloped roofs, it may not be feasible to sweep the roof and here, the first good rain of the season will wash away all the mud and leaves and this can be drained and only the water collected thereafter can be collected and stored.


Dr. Indukanth S. Ragade
Ex-Vice-Chairman of Alacrity Foundations Pvt. Ltd.

6. RWH

Very simple and innovative.

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