Effective Rainwater Filter – For rooftop rainwater harvesting – Very low-cost, do-it-yourself filters

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SAMPATH S
Posts: 40
Joined: October 28th, 2014, 1:00 pm

Effective Rainwater Filter – For rooftop rainwater harvesting – Very low-cost, do-it-yourself filters

Post by SAMPATH S »

I have been a member of this group for about six years now and have been benefitted by the contributions of many members. However, I could not make any contribution to this group, which I would like to rectify now.

I am starting this thread as an avid rainwater user for almost six years now – 100% for every requirement (particularly drinking) – throughout the year. Yes, you read it right, I did not attempt a borewell at all, nor do I buy tanker water, I am also not drawing any water from the BWSSB Cauvery water connection (which I have been having for nearly three years now). I am a fan of rooftop rainwater.

I am neither a scientist nor an engineer nor have any experience in any activity associated with rainwater till six years ago, when I constructed my present house and started experimenting with use of rainwater as the main (only) source.

I fully endorse the view of one of the members when he says that with Rainy Filters, the yield is hardly 20 to 30%, the rest going out as reject water. Initially I tried filtering the reject water using Raintap popup filter, but soon ran into difficulties and had to substitute with a customized filter container fabricated for me and used double layer cotton cloth to filter the reject water. I carried on in this fashion for almost four years and then started experimenting with my methods and have now come up with my own filters. While cloth filters are fairly good, there are many difficulties and disadvantages, which I would not like to go into.

I have been seriously going through every article and method on rainwater filters and have found one or the other disadvantages/loopholes and in my opinion the filters developed by me has several advantages and of course a little bit of maintenance is involved, which, in my opinion, is very ordinary. Above all, it is least expensive and do-it-yourself.

I have been experimenting with the filters fabricated by me for the last nearly one year through light and very heavy rains and have got myself thoroughly satisfied. I would like to share details of my self-fabricated filters with this group members which I am sure would be appreciated and lapped up by them.

I have been instrumental over the last few years in helping several owners to install rainwater filters for storage and direct use. My recently developed filters have also found many takers and has been widely appreciated by many residents in my Ward (5 - Jakkur). Several hundred enthusiasts have visited my rainwater filters and many have adopted the same in their own way.

I am extremely happy with the quality of the rooftop rainwater filtered and stored by me using my self-made filters. The water has good clarity, has near negligible TDS and acceptable pH.

I have also applied for the BWSSB sponsored Jala Rushi Puraskar, which was to be awarded on the World Water Day (22nd March) this year, but still has not seen the light of the day due to the Covid pandemic.

I have a total storage of 50,000 liters, a small family, and I also practice minimal use of water and scrupulously avoid wastage. Thus once full, my requirements for the next 5-6 months are met easily and even scanty rains in between help me boost my storage.

In the next few days I would be presenting my self-made filters, which I have named as Effective (Rainwater Harvesting) Filter.
SAMPATH S
Posts: 40
Joined: October 28th, 2014, 1:00 pm

Re: Effective Rainwater Filter – For rooftop rainwater harvesting – Very low-cost, do-it-yourself filters

Post by SAMPATH S »

Effective Rainwater Filter (Contd.)

Everyone knows that rooftop rainwater harvesting for storage has three stages – Roof, Filter and Storage; each stage has its own importance. Before I get to the Filter, the other two stages are mentioned in brief.

Roof: To be kept as clean as possible. Garbage in – Garbage out. If the roof is not taken care of, then the quality of water would be affected and would put lot of pressure on the filter. Moreover, the filter is intended to filter out physical impurities only, i.e. any impurities dissolved in water cannot be filtered. It is highly desirable to avoid bird droppings, which naturally contain pathogens and can get easily dissolved in the rainwater. There are certain ways to mitigate this and would be discussed later, depending upon requests.

Storage: Depending upon usage, it is possible that rainwater is stored over long periods, sometimes several months and maybe even a year or two. Hence, it needs to be ensured that the sump covers are tight enough so as not to allow crawling insects to get into and also preferably at a height over the floor level to prevent entry of dirty water. The sump cover may also be kept covered by some opaque sheet so that no light enters and also to keep the insects at bay. Light is necessary for living organisms to grow and multiply and preventing light entry would help preventing growth of fungus, algae, etc. There are methods to disinfect stored water and also to measure to level of residual chlorine. This would be discussed depending upon requests.

FILTER: Coming to the actual topic, filters are the heart of RWH system and help in filtering out the physical impurities.

As is well known, first flush (i.e. letting out the initial rainwater which would naturally contain large amount of impurities) is a must. The outgo of first flush is generally controlled by a valve and is let out for ground water recharge (generally a pit). This also serves to route excess rainwater when the storage gets full. It would be a good practice to even make use of the first flush water by storing it in an appropriate tank for watering plants, washing vehicles, floor, etc., which I have implemented.

Presently in Bangalore, two rainwater filters are in the market (raintap pop-up filters I believe has gone out of market) – one is Rainway and the other is Rainy, the former is ruling the roost because of the cost advantage and familiarity with plumbers. Sand and gravel filters are extremely rare.

The commercially marketed filters are analyzed here from the view-point of users and not to criticize or find fault with the products. Each product has its place.

The commercial filters are enclosed in a black container and people generally presume that once rainwater passes through the filters, the output is clean water. Unfortunately it may not be so. Be it the commercial filters or any other type of filter, what matters is the size of hole of the filter mesh / sand gap, which is generally measured in Microns (one Micron = one thousandth part of an mm-millimeter or one millionth part of a meter). The lesser the Microns, more effective the filtration is. Further, the measurement in Microns is the length/breadth of the square hole, the actual area of the hole is the square of the length/breadth. Thus the area of a 100 microns mesh is 100x100 or 10,000 square microns or 0.01 sq. mm.

Rainway filter is reported to have a hole size of 240 microns or an area of 57,600 sq.microns. Compared to this, the Rainy filter has a hole size of 250 microns or 62,500 sq.microns.

Thus before analyzing any filter mesh, please note the area of the mesh hole.

The lesser the area of the hole, it can withhold smaller particles. At the same time, as the area of the hole goes down, the filter can get clogged faster and may even stop filtration of water altogether. This is the reason to keep the rooftop as clean as possible.

Many of us have a feeling that dust is the only or the major impurity on the rooftop and gets out in the first flush. This is not true. Rooftop is also the place for innumerable number of ants and insects (live and dead). This is apart from bird droppings, which even sticks to the rooftop and difficult to clean. Even after the first flush a lot of them remain on the roof and continue to get added even during rain.

In case of Rainway filter, soon after the first flush, these insects are withheld in the filter chamber. The hole area of Rainway filter is sufficiently large to allow some smaller insects (live or dead) to enter. The bigger ones held in the filter mesh also get soft and dismembered in the presence of water, and enters the sump. The users are totally unaware of this. These organic matters entering the sump can obviously decay in due course.

Coming to Rainy filter, the holes are comparatively smaller but still sufficient to allow some impurities to get through. But there is no withholding of impurities as the un-filtered ones pass out along with the reject water. However, due to the way of construction, the Rainy filters throw out a substantial quantum of reject water, which in my personal opinion is much on the higher side, thus depriving the user of large quantity of usable water. The major advantage of the Rainy filter is its self cleaning character and hence involves least maintenance.

Most of the other kind of filters like sand/gravel filter, sponge filter, etc. tend to retain the fine filtered impurities and dead/dismembered insects, etc. These insects/organic matter decay and finally end up in the filtered water, besides the decaying/rotting can give rise to bad smell. It is virtually impossible to clean the entire sand filter on a day to day basis (when it rains), even though Netlon mesh, etc. are installed. Moreover, the gap between the sand is also substantial, but since we are not able to see or measure it, we take it as virtually water-tight. The actual users of this type of filter may be in a better position to throw more light on this.

Because of all the above, the simplest, easiest and the measurable filter medium remains as mesh only. Because of the need to filter water, materials which are not affected by water would need to be used in the entire filter. Thus the containers are generally made of plastic/HDPE, which are light weight, sturdy, easy to handle and won’t rust. The filter mesh is essentially made of Stainless Steel of 304 grade and above, which do not acquire rust and are also very light weight and strong.

The filter fabricated by me uses the above materials only.

Effective Rainwater Filters:

Effective Rainwater Filters enable you to filter 100% of rooftop rainwater (excluding the first flush, or you may in fact not carryout first flush itself if you badly need water as the filtration efficiency is fairly high).

Two types of Effective Filters:

I have fabricated two types of filters, the Type 1 is fairly easy to make and Type 2 is more advanced and the containers used need to satisfy certain criteria. To begin with, Type 1 is discussed and Type 2 later on.

To enable do-it-yourself using the extensively available containers, empty 20 liter paint buckets are chosen. Paint buckets are also very sturdy and can withstand rough use. Being plastic, it is amenable to cutting easily. The filter material is 304 grade Stainless Steel mesh, which accounts for the major cost.

Single and Multi-Stage Filters:

There can be one or more stages of filtration. More the number of stages, finer filtration can be achieved. It is preferable to have two stages, while 3 or 4 stages may also be attempted. I presently use a three stage filtration, though I have a provision to rapidly expand it to 4 stages.

The single stage filter mesh is of 75 microns, i.e. 5,625 sq.microns or 0.0056 sq.mm. This works out to be 1024% of the filtration efficiency of Rainway filters and 1111% of the Rainy filters (plus 100% filtration).

If you would like to have two-stage filtration, you may add one more stage for pre-filter for bigger particles like leaf, etc. using a mesh of much bigger size like 1 mm square or so. This would prevent frequent clogging of the 75 micron filter.

If you would like to have three stage filtration, then post (after) 75 micron mesh filter you may go for 50 micron mesh filter.

If you would like to have four stage filtration, you may go in for 37.5 microns or even 25 microns mesh filter.

I have fabricated filters with all the above mesh sizes, but find the last two sizes of 37.5 and 25 micron meshes are very sensitive and are likely to get clogged very frequently, particularly when it rains heavily. However, they would be of use in case of occasional light rains, when the impurities would be much more.

The cost of finer meshes increases steeply and hence would be of academic interest only.

The single stage mesh of 75 microns is the one that is advocated and a pre-filter mesh of about 1 mm for the two-stage filter would be good enough.

COST ANALYSIS OF MESH (for Type 1):

The 75 microns SS 304 grade mesh costs about Rs.1200 per square meter plus 18% GST, making it Rs.1416. This can be cut into 9 pieces, each of about 1 ft x 1 ft, making the cost of each piece at about Rs.160.

For the pre-filter, SS 304 grade mosquito mesh (small size) which is of about 1 mm can be used and 1 ft x 1 ft. is generally available at Rs.30 to 35.

Finer meshes of 50, 37.5 and 25 microns are progressively steeply costlier and may be considered only if one can afford and wants to experiment.

Additional cost involved:

For each stage of filter, you will need a PVC collar (generally 75 mm is sufficient) costing about Rs.35 and a little M Seal epoxy adhesive (costing about Rs.25 to 50).

For the basic filter (Type 1), two paint buckets of 20 litres each and a lid for each stage, which are generally available with many or can be procured at a small cost.

In addition you may need MS angle stand and miscellaneous items like screws/rock bolts.

Details of fabrication of the filters would follow.
Last edited by SAMPATH S on October 26th, 2020, 8:10 pm, edited 2 times in total.
SAMPATH S
Posts: 40
Joined: October 28th, 2014, 1:00 pm

Re: Effective Rainwater Filter – For rooftop rainwater harvesting – Very low-cost, do-it-yourself filters

Post by SAMPATH S »

Fabrication of Type 1 Filter:

The following steps describe the way I have fabricated the filter. For each stage, two 20 liter empty paint buckets are used.

Take one bucket; turn it upside down. Then perform cuttings in the bottom as per picture below:

Image

(To open images, please tap / right click on the image and open in a new tab or download the image)

Note: Images appear here in subsequent posts, as requested by some viewers.

Now take the SS mesh. Place it from inside the bucket cut as above and trim the excess mesh after ensuring that the mesh is placed perfectly flat at the bottom and ensure at least 0.5 to 1 inch mesh is projecting from the bottom on the side throughout the circular portion. This will ensure that the mesh could be securely pasted along the sides. Once you are satisfied, paste the mesh to the bucket using M Seal Phataphat (fast curing) epoxy adhesive (or any other adhesive you think would suit the purpose). Ensure that you mix smaller portions of the adhesive so that it does not get hardened during the pasting process. Allow a minimum of 4 to 8 hours for the adhesive to get hardened.

The mesh, upon pasting, would look as under from inside and outside:

Image
Image

Now take the other bucket. Also take the 75 mm PVC collar. Reverse the bucket and at the bottom middle make a circular mark using the collar and cut a round hole so as to just snugly fit the collar. Push the collar inside the hole so that it just gets into the bottom of the bucket and fits so as to be plain from inside. Now using M Seal adhesive as described above, paste the collar securely from the bottom and if necessary, gently from inside also. The finished bucket would look as below:

Image
Image

After allowing for about 4 to 8 hours for the adhesive to completely set, place the bucket with the mesh inside the bucket for which the PVC collar was fixed. Your filter is now ready and would look as under. You may cover the mesh bucket with a lid in which a suitable hole for the entry of rainwater is made.

Image

For the second stage of the filter, similar method is adopted. If more stages are desired, they may also be fabricated similarly.

Each stage of the above filter is mounted on MS angle stand fitted to the wall. A picture of the MS angle stand:

Image

The inlet pipe of rainwater is allowed into the first (or may be the only) stage of the filter so that it just comes to the top level of the filter mesh bucket. This is done to ensure that the rainwater hits the filter mesh with good force due to which the impurities collecting at the filter mesh are pushed to the sides and the middle portion will be kept clear to permit the filtered water to flow out. This repeats for each further stage. The PVC collar of the last stage connects to the piping which leads to the storage sump. This arrangement permits each stage filter to be pulled out easily for the purpose of cleaning the filter mesh.

The filter mesh is cleaned after each rain so that fresh impurities may be filtered easily and there is no possibility of the impurities decaying over time.

The following pictures of a two stage filter unit fabricated and installed by a rainwater enthusiast:

Image
Image

Type 1 filters work smoothly for roof areas of around 1000 sq.ft. and can withstand heavy rains.

If the rooftop area is substantially more, say 1500 to 3000 sq.ft. and even more, Type 2 filters would be necessary.

Detailed method for fabrication of Type 2 filter would follow.
Last edited by SAMPATH S on October 14th, 2020, 11:57 am, edited 2 times in total.
SAMPATH S
Posts: 40
Joined: October 28th, 2014, 1:00 pm

Re: Effective Rainwater Filter – For rooftop rainwater harvesting – Very low-cost, do-it-yourself filters

Post by SAMPATH S »

Fabrication of Type 2 Filters:

Type 2 filter resembles Type 1 filters for most aspects, except a few, which are mentioned below.

In this filter, in addition to filtration mesh at the bottom of the bucket, meshes are also fixed on the sides of the inner bucket as to allow filtering large quantity of water and permit holding more impurities and hence this filter can cater to roof areas of up to about 3000 sq.ft.

The outer container (bucket) is slightly bigger than the inner one, i.e. when the smaller container is placed inside the bigger container; there should be a gap of at least one inch throughout the sides and at the bottom about two inches. Any set of containers may be chosen keeping this aspect in mind. This aspect forms the basis for this filter type, which allows large quantity of water to be filtered and can tolerate more volume of impurities.

Retaining the same 20 liter empty paint bucket for the inner container, I have used a slightly larger paint bucket (which I could luckily get from a scrap dealer, but could not find one subsequently). Cuts are made in the inner bucket along the two sides in such a way as to easily paste the mesh of size approx. 1 ft. x 1 ft. that has been cut and kept ready. Please allow about 1 inch on each end for the purpose of pasting. If you feel so, the cuts may be made retaining a rib or two horizontally for greater support to the side meshes.

Image of a bucket cut along the sides (in addition to the cuts at the bottom) is given below.

Image

Image of outer bucket used by me:

Image

After pasting meshes in the inner bucket on bottom and both sides, it would look like this:

Image

After placing this in the external bucket, it would look like this.

Image

Fabrication of Type 2 RWH Filter is complete.

Fabrication of multiple stages and installation information applicable to Type 1 filters are equally applicable to Type 2 Filters.

A video of filtration using 3 Stage Type 2 filters made during heavy rains:

https://drive.google.com/file/d/1vuwyBGj1DRHkP6F3pcbuoL7uFO5Z1DWP/view?usp=sharing

A picture to show the quality of water collected in sump:

Image

This completes the information on fabrication, installation and working of the Effective Filters.

Would be happy to have the feedback from learned members of this forum.
Last edited by SAMPATH S on October 14th, 2020, 6:05 pm, edited 1 time in total.
SAMPATH S
Posts: 40
Joined: October 28th, 2014, 1:00 pm

Re: Effective Rainwater Filter – For rooftop rainwater harvesting – Very low-cost, do-it-yourself filters

Post by SAMPATH S »

In case of larger roof areas, like in apartments with a single down pipe, parallel processing is recommended.
SAMPATH S
Posts: 40
Joined: October 28th, 2014, 1:00 pm

Re: Effective Rainwater Filter – For rooftop rainwater harvesting – Very low-cost, do-it-yourself filters

Post by SAMPATH S »

The cost of a two-stage type-1 filter can be recovered in one good rain itself.
SAMPATH S
Posts: 40
Joined: October 28th, 2014, 1:00 pm

Re: Effective Rainwater Filter – For rooftop rainwater harvesting – Very low-cost, do-it-yourself filters

Post by SAMPATH S »

If anyone is interested in having a demo of the filters in use, please send a private message.
SAMPATH S
Posts: 40
Joined: October 28th, 2014, 1:00 pm

Re: Effective Rainwater Filter – For rooftop rainwater harvesting – Very low-cost, do-it-yourself filters

Post by SAMPATH S »

As a thumb rule, in Bangalore you can expect 1 lakh liters per 1000 sq.ft. roof area. Using the Effective Filters, you can enjoy 100% highly filtered pure water.
Visualizer
Posts: 199
Joined: June 1st, 2018, 6:24 pm

Re: Effective Rainwater Filter – For rooftop rainwater harvesting – Very low-cost, do-it-yourself filters

Post by Visualizer »

Informative thread Sampath.
The pictures are not visible in your post.
Is there some alternative method you can use to post pictures?
May be you can post this as a blog on social media site and link it here.
SAMPATH S
Posts: 40
Joined: October 28th, 2014, 1:00 pm

Re: Effective Rainwater Filter – For rooftop rainwater harvesting – Very low-cost, do-it-yourself filters

Post by SAMPATH S »

Thank you Visualizer for your feedback.

As there is a restriction for posting images in the posts (I think maximum 80 kb per post), it was difficult for me to post the pictures here. Hence I have given the link to the pictures, which can be accessed by opening the images in a new tab and I have actually mentioned about it.

However, in order to help some who may not be able to open the images, I shall furnish them here, in separate posts. The clarity of posts would be limited due to the limited size permissible.

Do give your feedback after having a look at the images.
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