Sunday, July 24, 2011

Rooftop Rainwater Harvesting - how I have done

I like this logo!

In 2008 I had contributed an article on rainwater harvesting for a garden website.  Read it here in this link. (Click on it).  There are many pictures showing how I began to do with crude methods using mostly available-at-home materials with little or no investment.  But the purpose was served for the time.  I have also given some basic information about the subject there and so repeating here would only amount to duplication. So, please visit that link.

The amount of rooftop rainwater that can be collected during a season can be estimated using this calculator in this link:
or here:
Here is an interesting site.
You can view your house rooftop using Google's satellite imagery to calculate the catchment area!

Mysore's rainfall is about 80cms. per annum (in about 52 rainy days).  If it falls on a 1000 sq.ft. roof area and the whole lot is collected, it would amount to about 1,88,640 litres of water, which is a lot of water!  It is calculated @1 inch of rain on a 1000 sq.ft. area will have 2358 litres.

I collect from a rooftop area of about  380 square feet into the sump through filters. Using that calcuator, I get about 65,000 - 70,000 litres per annum. A rough figure from wastage from 'first flush' deducted. The sump capacity is about 7000 litres.  We will be using municipal water supply usually but during the regular rainy season, I stop the supply and utilize rainwater which keeps topping up the sump. Without watering the garden our daily consumption would roughly be 500 litres.  I do not use the hose pipe to water plants, nor do clean the car and vehicles with it.  I also collect directly from other spouts in barrels and use it for gardening. If it is more than sufficient for gardening, I divert it to the main sump by which time, water will be clear of sediments. Since we do not use it for drinking or cooking at present, I have allowed both to collect in the common sump.  If space affords, a separate sump exclusively for rainwater is the best option.  One can also make a partition in the sump.  Bigger the capacity, the better.  

In the yard.. helpful for gardening
 PET bottles can be useful as it has many options like that!
 Simple direct collection on the balcony.
 PET bottle again. It has many options for angles!
 Collection from 3 spouts at a single point. Small balconies above bays.
 In the open yard - they can be used to flush the bath and toilets (requires carrying by hand, but it saves flushing and hence, pumping up from the sump). This part gets a lot of water.  The extra outflow runs out into the yard.
In the open yard again... more collection.  Useful for washing clothes (after all the particles settle at the bottom and the water is clear) and flushing the drain or gardening. Water must be emptied within 5-6 days to prevent mosquito breeding as it stays open.  This area no longer gets the flow because of some renovation.

My high school classmate and friend Ramesh Kikkeri who is an organic farmer and environmentalist, suggested me to try a full sand filter that works from the bottom.  So tried it.

It works on this line:

It worked well for sometime, but there was clogging of the central inlet pipe sooner than I expected and removing it for cleaning was quite cumbersome. It was supposed be easy, but even if I flushed the water from the bottom, the clogging was too much and it did not drag down the particles.  So it was time to have a rethink. I met U.N.Ravikumar who along with Ramaswamy was among the first to implement rain water harvesting methods in the city.  I invited him to take a look at the system.  He saw all the other crude methods and suggested me to go for a fixed system.  It was enough inspiration.  So, upon his suggestion, I replaced the 'Ramesh filter' with the new one which that worked with gravity (inlet from top and outlet from bottom).  I procured the filters from one Gururaj, though I could have made them myself.  He made the first flush and the sand filter for me, including stones, sand, net, sponge and all fittings for the barrel.  He charged a reasonable Rs.1,300/-. See next part.

Rooftop rainwater that flows down carries many particles.  I found out that in our house and location, the dust particles are way too much, reasons being the closeness to a road with heavy traffic and old gabled roofing.  Such dust is called 'fugitive dust'.  It is almost amorphous. The 'Gururaj set' with one 'first flush' was insufficient to cope with and it quickly clogged the main sand filter.

Look at that!  It's too much.  You can't see the blue sponge, now clogged up with particles!  Picture taken during a heavy downpour.

The first flush is like this, inside:
There is a plastic ball inside the holed pipe. It blocks when the barrel fills to that level and all the water that flows thereafter will flow into the main filter.   This barrel will hold up heavier particles.  Flushing this often esp. during a rain will help keep water cleaner.

This is the 'improved' set of filters.  The first flush tank is seen at the back. It collects the first flow.  This picture was taken in unused condition when I set it up. The main sand filter is topped by sponge layer 1" thick.

Later, I added one more filter using a sponge to reduce the load on the main filter. When it is raining, I wash this sponge often esp. in the first few minutes so that dirt does not escape to the main filter and quickly clog the sponge layer there.

It is collected in a small bucket.  I have made a 3" diameter hole in its bottom. I keep it on a collection basin which I have made too.  You can observe how I have cut the hole in steel and fitted a pipe to it. This is similar to the one to which the conical mesh is fitted at the first stage.

The picture below was taken when it actually rained and water is flowing through the down spout, conical mesh, first flush, first sponge bucket filter and then into the main sand filter.
This system was insufficient to keep out the fine dust particles and even some chips of cement paint (old house with lime plaster) that collects on the crevices of roof tiles and other corners and they flow down with heavy rain.  They seem to mix up almost continuously for a longer period.  The main sand filter clogged too quickly which resulted in overflow and wastage of rain water before filtering.  So what did I do?

I added a 'second flush' in between the first flush and the main filter so that clogging of the sand filter is further reduced, also its maintenance.  I bought a recycled barrel (30L, food grade) and removed its lid to use my own. See it in the picture below. Luckily, it was a barrel that previously contained enzymes for agriculture and narrowish, suitable for my purpose. The higher it is, the better the chances of the heavier particles of dust staying down!  The inflow to this fills up from the bottom through a pipe with holes in the bottom. This is to reduce splashing which would disturb the particles and aid in its escape from the top.

This is how the new filtration set is: 
See below, how the conical mesh filter at the initial stage works in holding back bigger particles which can be leaves, little twigs etc. In our case, there can be a lot of caterpillar poop (like tiny mustard seeds).  Those hairy caterpillars abound the city in the rainy months, more in old houses with gabled roofing.  Some live beyond and their poop come down with the first rain many weeks later - as you can see here.  We use the water that gets collected in our main sump only for washing purposes.  For drinking, we collect the 'municipal supply' directly in the mornings.
This has to be removed manually.

This is what I made for the 'lid'. This barrel would fill from the bottom and 'overflow' into the sand filter, leaving behind more heavier particles at the bottom. The force will make some finer particles to escape and we cannot stop it.  An old plastic bucket bottom was cut up to fix the pipe as here.  After one rain, I saw that it worked nicely as you can see particles stopped here before entering the barrel.  

 This is how the second filter gets its inflow. Observe the sediments trapped.  Picture taken during a heavy rain. I have aligned it in such a way that water first falls into the bucket area and then overflows into the central pipe and also through the holes, into the barrel. The brim of the cut up bucket is higher than that of the central gray (inlet) pipe.

Lots of debris trapped!  Otherwise, it would have gone further to clog the sponge and sand.  Now I can remove it easily from here!
This is how dirty water can be in the second filter.  With continuous rains, it will be progressively cleaner. You can see the pipe that allows overflow diverted into the sponge bucket filter which is actually the inlet for the main sand filter.

Picture below shows the valve to flush out dirty water from the bottom (cleaning purposes).

Let me now show how the main sand filter is made.  It is a 100L barrel, sufficient for the volume of inflow for my location. Bigger the catchment area, bigger the filter volume.  Inflow pipe on top right and filtered outflow pipe with holes at the bottom.  90mm pipes are fine for my location. 

The bottom is filled with stones up to the level of the holed pipe, which is about 6 inches from the bottom.

Fine Nylon mesh is used to hold sand. See the fingers for comparison of mesh size.

The clean coarse sand 'bundle' is kept on the stones. 

We can tie the corners of the nylon mesh for easy removal.  The second bag will be placed on top of it and then comes the sponge. 

In the meantime, I also learnt that dividing the sand into two parts will help easier removal for cleaning as it would also be lighter to lift up. So I put one half in another separate mesh bundle. The sponge on top will hold up the escaped particles and when they further escape, the first bundle catches them.  So it will be the first bundle that would require cleaning up more often. 

In this picture I have removed this sand bundle out for cleaning. You can see the dark colour which is nothing but fine dust which prevents good filtering and causes clogging.  The gaps between sand particles are extremely tiny.

This is clean, coarse sand. See the difference in colour.

Since this sand is coarse, we can clean it easily by rinsing it in a bucket of water a few times. On the right bucket (pictured below) you see it darker. It is the first step of cleaning.  Running the fingers or some implement to stir the sand while in water, will remove the very fine dirt (which is actually fugitive dust).  Pour the 'dirty water' out (may be into some plant bed).  The left bucket is cleaner sand as it is waiting for one more rinse. This should be done till stirring brings out no further floating particles and this sand can be put back into the nylon mesh.

This is cleaned sand ready to be put back into the mesh. You can observe the colour difference with the above picture.

The filter is asking for cleaning when we observe an overflow from the top even during a moderate rain and by observing a thin outflow into the sump.  It means the sand filter has clogged.  This operation could be necessary about twice a year or more depending on the amount of dust in that area.  Cleaner surroundings may require less cleaning. 

We get crystal clear water.  If rooftops are clean and well maintained, the water is potable. Many who are practicing it vouch that they use rainwater for drinking also (tastes wonderfully - water is 'tasteless'?) which is supposed to have cured some ailments too, besides rainwater-cooked food being tastier and vessels remain free from scaling. It is the purest water we are letting go by.  Catch it, it is free.  In some states of the USA, there are laws to prevent such collection!!

One thing that is yet to be done by me is preventing runoff.  

Runoffs could be diverted into wells or pits - not into drains!  But in our case, we have to divert at present into the open drains - to flush out man made garbage - in the absence of regular cleaning.  There is a worse picture which I will not show here!

During childhood I used to play in the rainwater that flowed near road kerbs and floated paper boats in the fast stream that eventually flowed into storm water drains.  Many times when it rained after my school, I used to walk home making the feet with shoes and socks wet in such roadside streams soon after the heavy rains.  It was such fun, but did not realize that it was awful to wear the shoes the next day!  As I grew up, I began to wonder how much water went down the drains. 

It is time the citizens realized the value of water.  It is a horrible sight for me to watch the servant of a rich family (there are many who do this without a care) close to our house use a huge hose pipe every morning to clean the owner's two cars and the pavement next to their compound!  Water floods the road! 
Harvesting and conserving water is every individual's duty.
Every drop of rainwater is precious - save it.
It might be the very drop that will quench your thirst one day.
Collection of rooftop rainwater is easy and not expensive! Let's do it - when we can wherever we can!



0s0-Pa said...

Very unique photos of the inlet filters for harvesting the rainwater - thanks for taking the time to post them all!

Kumar Sharma said...

Dear Dinu, Very resourceful indeed! You have put in a lot of effort and done an excellent job of the rain water harvesting. You are a very active person and are always thinking of something useful and also share with others -as per your motto of 'Live and let live'. With all the good photographs, it is a pleasure to go through your blog and learn. But not many will be active enough to actually put in practice - quoting, maybe, various types of excuses & constraints. But yoiu have shown that where there is a will there is a way! Thanks, Kumar.

BV said...

Excellent and wonderful ! I will ask my contractor to implement this in our house (under construction). If he tries to avoid, is there someone in bangalore who has done this and help me ? Or someone who has done this here that I can look as well ? Thanks

Dinakar KR said...

Thanks BV.
I have seen two people doing it in a beautiful way. They never depend on public water. They have planned and built two separate sumps, one exclusively for rain water - with a large capacity - and one for public water. One season's rain is good for use all round the year - they use for cooking and drinking. Also the roof slopes are planned towards the down spouts which easily leads to the sump. They have kept the filter on the first floor and maintaining the filter is the only real job. There are only benefits in implementing this and is extremely useful in areas having water scarcity. Planning ahead helps in doing it effectively. It can also be done in old constructions also.

Sachin Chindu said...

Great work sir, discribed very well . As RWH is manditory in banglore ,there are many filters available , how diffrent is your filter need to know , can i meet you sir, MY self Sachin , BE Environmental science from SJCE , wroking with IISc .

Dinakar KR said...
This comment has been removed by the author.
Dinakar KR said...

~Sachin Chindu | Thanks. Write to dinakar58ATyahooDOTcom if you want to visit. Introduce yourself in some detail if you write.
I know of different types of filters available in Bengaluru, but we have to make the ones that suits our location. Best wishes.