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

[SAMPATH S]

FILTERS (Contd.)

Type-2 Effective RWH filter fabrication:

Type 2 filter fabrication is very similar to that of Type 1, with a few modifications.

For each of the inner filter buckets, similar 20 liter paint buckets are used. Only difference is that in addition to the filtration mesh at the bottom, mesh is also pasted along the sides. Approximate measurement for cutting along the sides may be about 8 to 10 inches. These measurements are approximate and may vary slightly from case to case.

Inner bucket cut along the sides also:

Type 2 inner bucket slots cut bottom and sides inner view.jpg (74.65 KiB) Viewed 34593 times

Type 2 inner bucket slots cut bottom and sides bottom view.jpg (102.9 KiB) Viewed 34593 times

[SAMPATH S]

FILTERS (Contd.)

Inner bucket with mesh pasted along the sides, in addition to bottom:

Type 2 Filter with mesh pasted inner view.jpg (169.36 KiB) Viewed 34592 times

Type 2 pre-filter mesh pasted inner bucket.jpg (293.83 KiB) Viewed 34592 times

[SAMPATH S]

FILTERS (Contd.):

The outer bucket used is of a larger size, say about 25 liters. Due to this, the inner bucket would completely sit inside the outer bucket, which will not allow proper outflow of filtered water. We need to suspend the inner bucket from the outer bucket, allowing a gap of atleast half an inch along the sides and at the bottom about 2 inches. This is done by fixing a pipe of suitable dia along the rim of the inner bucket, so that the desired suspension is achieved. The outer bucket is so chosen that it has a gap of about half inch to maximum one inch around the inner bucket.

In my present model, the gap is close to 1 inch. Hence I used the washing machine outlet pipe to achieve the necessary suspension. This pipe has a dia of more than 1 inch.

IMG_20210427_172054076.jpg (204.95 KiB) Viewed 34589 times

Picture of the Type-2 Effective RWH filter wall mounted presently being used by me.

Type2 Filter system wall mounted.jpg (33.32 KiB) Viewed 34589 times

This completes fabrication of Type-2 filters.

[SAMPATH S]

FILTERS (Contd.):

Other aspects:

Point to note that the inlet pipe to the filter should be at the center of the filter bucket. If not there may be frequent occurrence of blockage.

Rain water is made to fall through the pipe routed (as described in the piping section) from a height vertically into the pre-filter. The pipe is made to just enter the pre-filter bucket (and no further). The water falling with great force from a height automatically pushes the impurities to the sides of the bottom filter mesh keeping the center portion free for filtration and the filtered water is routed to the fine filter in a similar way. This dynamics of water falling at force from a height helps the filter to avoid blockage at the middle of filter mesh.

After filtration through the 75 micron fine filter, the filtered water goes to the sump tank. To the collar of the fine filter, a piece of 75 mm pipe is attached (without pasting). This pipe connects to the 75 mm elbow (bush/washer type), the washer of which is removed to facilitate easy assembly/disassembly of the fine filter. The pipe further leads to the sump tank through appropriate piping. Pictures of my installation below:

Filter outlet to sump pipe.jpg (186.11 KiB) Viewed 34589 times

Filter to sump.jpg (258.6 KiB) Viewed 34589 times

Both the pre-filter set and the fine filter set of buckets can be easily pulled out for the purpose of cleaning. Please note to clean the impurities collected in the filter meshes, along with the outer buckets regularly everyday when it rains. If the impurities remain they may start decaying and may contaminate the further rainwater, besides possibly blocking the filter mesh.

To facilitate cleaning of the buckets easily and to reduce the water used for cleaning, one may use a faucet jet, preferably placed near to the filters. By directing the jet water appropriately, the filters can be cleaned fairly quickly.

The filter buckets are made of plastic. Hence it may be necessary to ensure that it is protected from direct sunlight. Further, shading the filter unit area would also help one to monitor the filtration aspects even during heavy rains.

With this, the fabrication part of the Effective RWH Filter is complete.

To get info about the fillter, also refer to my following videos:

https://www.youtube.com/watch?v=2yO3Q2-5SEo

https://www.youtube.com/watch?v=qyOxuX_ZloA

[SAMPATH S]

SUMP:

After filtration, the pure filtered water is stored in the sump tank. Underground sump tanks are preferred to over-ground storage. Sump tanks generally have large capacity, besides not utilizing usable space. Moreover sump tanks have very little possibility for penetration of light, since the sump lid is mostly situated in a covered place. Further sump with today’s set up of automatic water level controller which also has indicator to know the approximate water level in the sump, necessity for frequent opening of the sump tank lid is greatly minimized.

It is better to have the sump tank lid as tight as possible not only to avoid possible entry of light (which can lead to algae formation and also support living organisms which would certainly contaminate pure water), it would also greatly minimize the entry of crawling insects. As an additional safeguard, one may cover the lid with an opaque synthetic sheet, which would, in addition to eliminating possibility of light entering, also further minimize chances of entry of crawling insects.

Desirable sump capacity:

Many house owners, especially those who want to store rainwater, are confused about the desirable capacity of sump to be built and the number of sumps/partitions. There are multiple sources of water available like tap water (also referred to as Cauvery water in Bengaluru), bore well water / tanker water besides rainwater. There are also queries as to which of these waters can be mixed without compromising on the quality and also what could be the sump capacity desirable for rain water.

Rainwater, if collected with reasonable diligence, would be highly pure than any other source of water. Hence mixing of water from any other source may only reduce the quality of rainwater and not vice versa. Generally water from bore wells/tanker tends to have high to very high TDS (total dissolved solids), while TDS of rainwater is generally negligible. TDS of tap water mostly lies within this range.

For a rooftop area of 1,000 sq. ft. with an annual rainfall in the range of 100 cms., (generally Bengaluru has rainfall around this range), the rainwater annual yield would be around 1 lakh liters. Since it rains heavily during monsoon and sometimes during pre-monsoon, if one has a large storage, most of this rainwater could be stored and put to domestic use.

Storage for rainwater also depends upon the water usage which in turn depends on the number of persons residing in the building. With economical usage of water, per person per day usage may be taken to be roughly 125 liters (sometimes it is taken as 100 liters also, this is slowly being brought down to 80 liters as potable water is getting scarce). Thus if there are 5 persons residing and taking the daily per-capita water usage at 120 liters, the daily requirement may be approximated to 600 liters. Generally there may be a maximum of 100 days between two rains, which works out to 60,000 liters. Since the cost of creating storage of this capacity would work out very substantial, besides issues regarding structural stability of the building, and due to possible availability of other sources of water, one may plan for a suitable capacity.

Also considering the size of the roof (catchment area), for a 1000 sq.ft. roof, a capacity of about 25,000 liters may be planned and for bigger areas suitably more.

It is always preferable to have this capacity partitioned into 2 or 3. One of these partitions may be used for tap water and the remaining for rainwater and in its absence for bore well or tanker water. It would be preferable to have the sumps linked to allow overflow of rainwater into others. Thus when rainwater is in abundance, one may not utilize other source/s.

Even after filtration using fine mesh (as in the case of Effective RWH Filter), there would be some amount of very fine sediment, which would settle down in the rainwater receiving tank partition. Overflow from this tank/partition to other tank/partition would be clear water. Thus inter-connection of tanks / partitions would not only help in storage of the desired source of water but also to the maximum available storage.

Picture of crystal clear rainwater stored in the adjacent sump partition (overflow from the rainwater inlet sump):

Clear water stored in sump.jpg (167.82 KiB) Viewed 33977 times

[SAMPATH S]

SUMP (Contd.)

Modification to rainwater sump inlet pipe:

Rainwater, even after sufficient first rain separation and fine filtration, may contain some amount of extremely fine dust (consistency like wheat flour), which makes the water somewhat turbid. Ultimately this fine dust settles down at the bottom of the sump, but it takes some time to settle on its own. This fine dust is inorganic and inert, i.e. it neither reacts with water nor dissolves in it (hence the TDS of rainwater is not affected), nor gives any foul smell.

Even after ensuring the incoming rainwater flows down into the sump softly, the turbidity of the incoming rainwater makes the stored clear water also somewhat turbid again.

To reduce the effect of the mix up of incoming rain water and settled water, the incoming rain water can be made to flow directly to the bottom of the sump, without mixing up with the already settled clear water.

This can be achieved by attaching a pipe to the rainwater sump inlet. A picture of the attachment pipe is below:

Attachment to rainwater inlet to sump.jpg (25.55 KiB) Viewed 33977 times

Picture showing actually installed pipe:

IMG_20201121_125334110.jpg (120.47 KiB) Viewed 33977 times

With this, the incoming rainwater will cause very little disturbance to the already settled clear water. Since the incoming water is made to flow in the upward direction, the already settled sediment in the sump would also not be disturbed. The pressure of water column in the sump above the incoming rain water will calm it down and slowly distribute the fresh rain water at the bottom itself, and this would further help in quickly settling down the dust in the incoming rain water.

This installation needs to be attempted when the sump is empty or has sufficiently low level of water. I have adopted this model and am highly satisfied with the result.

[SAMPATH S]

SUMP (Contd.)

Floating suction to pump clear rainwater from top water layer of sump:

With the attachment to the sump inlet pipe already detailed, the settled clear water remains at the top of sump and the incoming mild turbid water settles at the bottom, the turbidity in which settles down much faster.

Nowadays pumping from sump to the overhead tank is done using submersible pumps (also called open well submersible pump). This pump is placed at the bottom of the sump under water. The suction generally takes place at a height of less than one foot from the bottom of the sump.

The bottom of the sump has settled down sediments and the incoming turbid water. Even though the water above is clear (after settlement), the pump tends to suck the somewhat turbid water and may be some sediments settled at the bottom.

To overcome this situation, a simple suction float helps in pumping clear settled down water from the top layer of the sump. I have successfully designed a suction float costing very less and with materials available from local shop. Same is pictured below:

Suction pipe with float.jpg (151.11 KiB) Viewed 33977 times

The suction float is connected to the suction inlet of the pump. A union is used to facilitate removal of the float for any possible repairs and re-fixing. The floating effect is achieved using an empty plastic bottle, preferably about two liters or more (sufficiently strong with a good cap). The attachment is made using cable tie. I have used a 1.5 inch flexible hose pipe. Also use hose clamps at both ends of the hose pipe so that the hose remains airtight. (Only one clamp is shown, but do use hose clamp at both ends, also use 304 stainless steel or aluminum clamps so that they stay rust free). Please ensure that the connections are air tight for a good suction effect. If the hose pipe is heavy, it might need a bigger sized bottle as float. A transparent bottle will enable you to confirm whether the bottle remains empty (without any leakage) always (otherwise the pipe would sink to the bottom defeating the purpose).

Picture of the actual installation:

20230127_174410.jpg (189.54 KiB) Viewed 33977 times

Additional points to be noted:

Attachment pipe (to suction inlet of pump) should be kept horizontal and should be at the level of the pump inlet or slightly inclined lower. In case the attachment CPVC pipe is inclined above, suction may get adversely affected and the pump may not suck water and the windings may be burnt, unless protective measures are in place.

Also at the time of initial filling of the sump, water may be allowed just above the pump level and some water is poured into the suction pipe, which would remove any air block in the suction. Air block will not allow water to be sucked and the windings may be burnt, unless protective measures are in place.

After the above exercise, confirm the suction is smooth (without any air blocks) and pump works normally.

Subsequent rise and fall in water level would not affect proper suction.

It is always advised to install Water Level Controller which would sense water being pumped and in case of any abnormality would switch off the pump automatically.

This floating suction has been tested by me and is working extremely well.

This exercise has to be carried out when the sump is empty or when the water level is sufficiently low.

[SAMPATH S]

SUMP (Contd):

Sump overflow pipe:

Many RWH enthusiasts, in their eagerness to store rainwater to the maximum, plan for sump overflow pipe, which could carry excess rainwater to a ground water percolation pit or to the storm water drain.

It is strongly advised to avoid this kind of overflow pipe from sump tank as one would have no control on insects, cockroaches and even rodents and snakes that may enter from the other side.

In case the sump tank/s get filled due to rainwater, it is better to open the first rain separator valve, which would stop rainwater flow to the filter and hence to the sump tank.

Cleaning of sump/s:

The sump in which rainwater is collected will naturally have fine settled dust at the bottom. It is preferable to clean this sump periodically. I generally clean this sump about 3 times in a year, when the water in the sump is nearly used up and there would not be chance of rain in the next few days/weeks.

As regards other sumps, I get a chance to clean them once a year. The water remains in pristine quality even after a year also.

Cleaning time is the best time to inspect the sump for any possible leakage points / cracks / leakages likely to develop. This is also the appropriate time to initiate preventive/corrective steps to avoid existing/possible future leakage issues.

[SAMPATH S]

OVERHEAD TANK:

Algae formation:

Generally houses have overhead tank. Majority of them are made of HDPE (plastic). A few are made of RCC.

A representative picture of the overhead tank is below:

air vent in water tank.png (74.97 KiB) Viewed 33168 times

Most of those who have seen inside the overhead tanks (especially in summer) would have observed that the sides of the tank have a deposit of algae, which is characterized by its greenish colour.

What could be the likely reason for this and whether this can be minimized, if not completely stopped?

Some of the tanks may not have the air vent marked as 1 above. Very few may not also have the overflow pipe marked as 3.

It may be notice that the air vent generally has a T fitted on top.

Growth of algae requires moisture (water) and this is accelerated by the presence of light. Since overhead tanks are exposed to sunlight, some light enters through the T of the vent pipes and also through the overflow pipe. The powerful sunlight partially gets reflected through these openings and this helps the growth of algae.

To drastically reduce the chances of sunlight entry, I have slightly modified the vent pipe as below:

Modified vent pipe.jpg (103.67 KiB) Viewed 33168 times

As you can see, to the T is added an elbow on both sides. This makes the outlet face the terrace and the chance of entry of sunlight is greatly reduced. This also makes it difficult for the feeble scattered light to enter the moist surface, greatly reducing the chances of algae formation. Please note that still algae might be present, but only in traces. I have confirmed this by making the change at my house.

Compared to river water and borewell water, rainwater by itself resists the formation of algae due to its ORP (Oxidation Reduction Potential) being positive.

[SAMPATH S]

Overhead water tank filter

Most of us are familiar with the following problems due to the presence of impurities in water:

1. Blockage in health faucet
2. Blockage in concealed flush tank
3. Blockage in tap aerator nozzles
4. Build up of sediments in the sediment filter in water purifier
5. Blockage in washing machine inlet
And other similar places in the pipeline.

Impurities enter into water from the source, i.e. tap water, bore well / tanker water / filtered rain water, besides cement mortar residues in sump, micro plastics, etc.

In newly constructed / renovated houses, the chance of presence of impurities/sediments is high.

All the above issues not only cause problems/annoyance/inconvenience, but substantial expenses for repair/service and in some cases replacement of parts/equipment, etc.

There is a simple way in which these problems can be drastically reduced.

This is by use of TANK FILTER / DOWN FILTER. This filter has a stainless steel mesh of size 130 microns (or 0.13 mm). This is a simple filter fixed either vertically or horizontally to the outlet pipe of the overhead tank, before distribution to the household fixtures/taps.

I am using this tank filter for the last three years and am extremely happy with it. It is easy to clean the impurities withheld by the filter. A picture of the filter is below:

Tank filter.jpg (242.49 KiB) Viewed 33167 times

These filters are available for various sizes of pipes like 0.75 inch, 1 inch, 1.5 inch, 2 inch, etc. Many brands are available on e-commerce sites.

This filter is to be used only with the overhead tank outlet and not in the inlet.