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

[SAMPATH S]

RRWHASIMS – Rooftop Rainwater Harvesting & Storage Integrated Management System

Piping:

Downpipe from roof carries the rainwater. This simple downpipe can be modified so as to serve various purposes to help in collecting rainwater.

Normally, the rainwater is routed to groundwater recharge pit through the downpipe from terrace. In some cases, it is sent to storm water drain. In this downpipe, for harvesting rainwater (for storage), a valve is fixed at about 3 or 4 feet above the ground level. This is called first rain separator valve. When this valve is kept open (which is generally done for allowing initial impure rainwater to escape and also when the storage becomes full), the rainwater flows out.

A couple of feet above the valve, a T joint is fixed, to route the rainwater to the RWH Filter. Additional tapping/s may be made as per individual requirements for various purposes. Also for sampling the quality of water, a tapping can be made above the first rain separation valve using a service saddle. Here are some pictures:

First rain separation valve & just above it a tapping for water sampling using a service saddle:

Service saddle with gate valve fixed above first rain separator valve.jpg (195.64 KiB) Viewed 42199 times

First rain separation: There are many interpretations regarding first rain separation. Some say that the first couple of rains should not be collected as the impurities would be large; others say that the valve has to be kept open for 5 minutes, other say 15 minutes.
To avoid all speculations and to know for how long the valve has to be kept open, the sampling outlet would be of great help. It is also known that those who have no other source of water and are in dire need of water, even the rainwater with some impurities would be of immense help. There are others who have other sources like groundwater, but here also when the groundwater level goes down precariously, some amount of impurities in rainwater (particularly during occasional rains in summer), would be tolerable. There are others who have access to multiple sources like tap water supply, tanker water, ground water, etc., for them clean water is the prime criteria.

The tapping above the first rain separation valve using the service saddle would be of immense help in such situations. Once the first rain separation valve is closed and the tap in the service saddle is opened, water flows out through it. This water may be collected in a bucket preferably with white interior and the water quality analyzed. Till one gets water of satisfactory quality to meet their requirements, the first rain separation valve may be kept open.

With this arrangement, one may decide the quality of rainwater they wish to collect, without any speculation.


Tapping for RWH filter; also for collection of unfiltered water for watering plants, cleaning, etc.

Piping to Filtration unit.jpg (83.02 KiB) Viewed 42199 times

Above the first rain separation valve, one may make a tapping using a T junction for collecting impure / pure water in a separate storage which can be used for watering plants, cleaning vehicles, floor and such other non-potable purposes. This is purely optional.

A little above this, the T junction tapping is used to route the water to the all important rainwater harvesting filter. I have used two elbows/bends to make the water rise and then connected to the RWH filter. This has been done deliberately so as to avoid any possibility of impure rainwater getting splashed through the pipe to the filter. One may also use a Y joint or any other suitable piping to achieve this objective.

In my installation, almost all the PVC pipes and fittings have not been pasted, but just push-fitted. I do not find any significant water leakage due to this. This arrangement, however, enables me to make changes whenever I wish to experiment, by pulling out the pipes and joints which can be reused. This is purely optional.

[SAMPATH S]

WORLD WATER DAY 2023:

22nd March every year is observed as World Water Day.

The theme for this year’s World Water Day is “ACCELERATING CHANGE TO SOLVE THE WATER AND SANITATION CRISIS”. Be the change you want to see in the world. You can make a difference by changing the way you use, consume and manage water in your lives.

Water touches the life of each and every human being !

A reminder:

To mark the occasion of World Water Day 2023 and as my small contribution in creating awareness on harvesting rooftop rainwater and to showcase a demo about my Effective Rainwater Harvesting Filters and also the Rooftop Rainwater Harvesting & Storage Integrated Management System being adopted by me, I plan to hold a session on Sunday the 19th March 2023 at 10.30 am at my house. Those interested in participating may send their request at the earliest. It will be purely on a First Come First Served basis. The numbers of seats are limited. Location details would be informed to the proposed participants individually. Non-members may communicate to my email id sampaths144@gmail.com.

[SAMPATH S]

FILTER

Filter is the most important aspect of rooftop rainwater harvesting. When rainwater harvesting is mentioned, invariably it means some kind of filter is used.

Much before the present mesh filters came into existence, gravel / sand / charcoal filter was in use. Even today, cheaper and crude filters use one or more of these materials filled in a pipe. The major drawback of this kind of filter is that there is no way to know the size of holes through which water might pass. Further, since rooftop contains bird droppings, dead and live insects, leaves, organic matter, besides the ever present dust, these get into the gravel and sand, remain there itself, decaying and decimating and ultimately gets into the filtered water. Generally, the sand and gravel is removed, cleaned and put back once or twice a year.

Most rainwater harvesters use the harvested and stored rainwater for ONLY SECONDARY PURPOSES. Hence they do not mind compromising on the quality of the stored rainwater.

If one intends to store harvested rainwater for all domestic applications, including drinking, cooking, bathing, etc., one needs to pay a lot of attention to an integrated system of which filter plays an important part. EFFECTVE RAINWATER FILTER is aimed at fulfilling this need.

There are a few commercial filters available and each of them has its own drawbacks. Added to this, all the filter meshes are of 250 microns (1/4 mm) or more and hence allow liberal amount of impurities to pass through.

After using some of the commercially available filters I was not satisfied with the quality of filtered water. I was continuously experimenting with various alternatives and finally could succeed with fine filter mesh of 75 microns.

It needs to be understood that in case of heavy rains and a larger roof area (catchment), the intensity of rainwater can exceed 5000 liters per hour. Keeping this in mind, the filter dynamics is designed and the optimum filter mesh size of 75 microns is chosen.

Size of the mesh mentioned above is one side of a square. The maximum size of the impurities that can pass through the square is its area (i.e. side multiplied by side). Thus the 75 micron mesh is more than 1100% efficient than a 250 micron mesh. Thus Effective RWH Filter mesh filters out most of the impurities and the collected rainwater would be of the best possible quality.

The filter fabricated by me has been named as EFFECTIVE RAINWATER HARVESTING FILTERS, or simply Effective Filters.

In the terrace (rooftop) at the place where the downpipe is connected, a grating with fairly large holes are placed, which effectively filters out larger particles like leaves, paper, plastic, etc. Most of us would have noticed that when such impurities reach the grating, they tend to block out the flow of water, resulting in flooding on the terrace. In case the staircase on the roof leads to any indoor place (as in the case of duplex houses or internal stair case or covered staircase room), the flooding might result in water entering these places and causing havoc. Terrace water accumulation might also harm the building. It would also result in rain water not reaching the RWH filter, resulting in loss of precious water.

In case it is decided to do away with this grating, all the larger impurities would land in the filter, thus blocking the filter almost instantly, again defeating the very purpose of rainwater collection.

To overcome the above issues the grating might be done away with and a pre-filter stage is used in the Effective RWH filters, and this stage has fairly large size mesh. I have used the insect screen mesh (SS 304 grade) generally used for sliding windows and it is roughly a 1 mm mesh. Even if there is a grating, the pre-filter stage would be very useful.

Picture of the insect screen mesh used by me for pre-filter stage:

Pre-filter SS 304 mesh.jpg (89.26 KiB) Viewed 41690 times

Thus, the Effective RWH filter is essentially a two stage filter, the first one being the pre-filter and the second stage is a fine filter (75 micron SS 304 grade mesh).

Picture of the 75 micron mesh:

75 Micron SS304 fine mesh.jpg (184.79 KiB) Viewed 41690 times

To drastically reduce the overall cost of filter and to enable the Do-it-Yourself aspect, the Effective RWH filters use empty paint buckets of 20 liters for the filter.

Thus, there would be 2 stages in each filter, the first one being pre-filter stage (using larger size mesh) and the second stage being fine filter stage (75 micron mesh).

Each of the stages need 2 buckets (placed one inside the other, inner bucket for fixing the mesh and the outer bucket for routing the filtered water), thus 4 buckets in all.

Further, depending on the catchment area (rooftop area available for rainwater harvesting), two classifications of filter are made, one generally for rooftop area less than 1000 sq. ft. (called Type-1) and the other above 1000 to about 3000 sq.ft. (type -2).

Type 1 filter has one filter mesh at the bottom of the inner bucket, while Type-2 filter has meshes at the bottom of the inner bucket and also along the side, to accommodate large quantity of impurities on account of the increased roof area. Because of this reason, the outer container (bucket) of type-2 filter has to be larger than the inner bucket and hence a 25 liter bucket is used.

[SAMPATH S]

Mesh preparation for pasting at the bottom of inner bucket:

The size of mesh used (both for pre-filter and fine filter) is about 1 foot x 1 foot. This mesh is cut into a circular shape (for pasting at the bottom of the bucket) to match the size of inner bottom of bucket with about half inch projection on the side (pasting is done along the side).

The method I have used for this circular cutting is below (It is done this way since it is difficult to make any marking on the mesh in the ordinary manner).

Take a thick plastic paper, preferably white, measuring about 15 inches x 15 inches or more. Place the bottom of the bucket on this. You can make the circular mark using a pen / pencil. To this circular mark add about quarter to half inch (on the outer) and make another mark. We may now cut the plastic sheet along this outer mark and this would serve as our reference. Refer picture below.

20220622_125014.jpg (295.21 KiB) Viewed 41689 times

Now attach this reference plastic sheet on the mesh using clips as pictured and cut off the extra corners to obtain a circular shape.

Then the insect screen mesh (cut into a circular shape to suitable size) is pasted from inside the bucket. For pasting of meshes, I have used M-Seal Phataphat (fast curing) epoxy putty.

M Seal Epoxy putty.jpg (124.26 KiB) Viewed 41689 times

To ensure proper adhesion, it is advisable to roughen the plastic pasting surface using sand paper.

[SAMPATH S]

Filter (continued)

Now let us get to know how these Do-it-Yourself filters are fabricated / made:

Let us begin with Type-1 Effective RWH filter fabrication:

In this, as already stated, 20 liter empty paint buckets are used, 2 (placed one inside the other) for pre-filter and 2 for fine filter, thus 4 buckets in all. In other words, the there will be two inner buckets and two outer buckets.

We need to cut slots at the bottom of the inner buckets and fix the filtration mesh.

Picture of an inner bucket with slots cut - top view:

Inner bucket with bottom slot cut inside view.jpg (157.91 KiB) Viewed 41513 times

Bottom view:

Inner bucket with bottom slot cut bottom view.jpg (185.24 KiB) Viewed 41513 times

Markings for slot cutting:

Bucket bottom slot cutting marked.jpg (114.25 KiB) Viewed 41513 times

[SAMPATH S]

FILTER (Continued):

Drilling holes for slot cutting:

Drilling holes for slot cutting.jpg (67.49 KiB) Viewed 41510 times

Slot cutting using a jig saw.

Slot cutting using Jig Saw.jpg (107.66 KiB) Viewed 41510 times

For making holes, one may use a drilling machine or make holes using any sharp objects like a poker, which may be heated a bit to facilitate quick poking.

The cutting may be done using a machine as above or with a hack saw blade slightly warmed or even a serrated kitchen knife, slightly warmed.

Picture with the insect screen mesh (pre-filter) pasted from inside, as seen from the bottom.

Pre-filter mesh pasted.jpg (320.35 KiB) Viewed 41510 times

[SAMPATH S]

FILTER (Continued):

Picture of the 75 micron fine mesh pasted (inside and outside views)

75 micron mesh fixed inner view.jpg (206.61 KiB) Viewed 41510 times

Type 1 Outer view of 75 micron mesh fixed .jpg (208.15 KiB) Viewed 41510 times

It needs to be ensured that the mesh should be flat at the bottom of the bucket. This is an important requirement.

In the remaining each of the two buckets (outer buckets), we need to fix a 75 mm PVC collar, picture below:

PVC Collar 75mm.jpg (174.12 KiB) Viewed 41510 times

[SAMPATH S]

FILTER (Continued):

To fix this, we need to cut a circular hole at the bottom of both the outer buckets. Circular marks are made using the PVC collar. To facilitate cutting, a hole is made inside the circle to push the blade/knife and cutting is made as mentioned earlier. The hole should be just enough to snugly push the PVC collar. For this, sufficient care needs to be taken, as any loose fitting would defeat the purpose.

Marking in outer bucket for circular hole cutting.jpg (195.71 KiB) Viewed 41507 times

Picture of the bucket with circular hole cut at the bottom:

Outer bucket with circular hole cut inside view.jpg (58.07 KiB) Viewed 41507 times

[SAMPATH S]

FILTER (Continued):

Into this hole, the PVC Collar is pushed from the bottom so that it is just flush with the inside bottom surface of the bucket. Pasting is done from outside to securely hold the PVC collar. From inside a thin pasting is applied. Any projection inside the bucket or too much of pasting from inside will result in water logging inside the bucket, which may gradually lead to algae build up.

Picture of PVC Collar pasted on the outer buckets: Bottom view and inside view:

Bottom view of outer bucket with PVC collar pasted.jpg (221.67 KiB) Viewed 41507 times

Inside view of outer bucket with PVC collar fixed.jpg (147.98 KiB) Viewed 41507 times

Then inner buckets are placed in the respective outer buckets. The buckets are wall mounted using MS angles fabricated into L shape, like the one below:

MS Angles fitted to wall for mounting filter.jpg (32.6 KiB) Viewed 41507 times

At the time fixing the brackets, roughly about 5 to 6 inches gap may be maintained between the two sets (of filter buckets). A small piece of 75 mm pipe may be inserted into the collar (please do not paste the pipe, it is not necessary to paste). The actual length of the pipe piece of the pre-filter should be barely projecting upto the top of the fine filter.

Both the filters may be covered by a plastic lid (with holes made at the center for entry of pipe) to prevent entry of dust or insects.

[SAMPATH S]

FILTER (Continued):

Picture of a Type-1 Effective RWH Filter, wall mounted:

Type 1 RWH Filter wall mounted .jpg (159.28 KiB) Viewed 41507 times