Rainwater harvesting - the need of the dayBy Dinakar KR (Dinu)
October 30, 2008
Being a hardcore and natural [!] nature-lover from the days of my early memories, I've observed how periodically rains came and how accurately they were predicted in our 'astrological calendars' (published annually at the time of our Lunar New Year). There has been an increasing unpredictability to the patterns, not only here, but in many parts of the world. Much is written but less done about the factors that affect this climatic change and it's become more noticeable, especially in the last decade or so. But let me not focus on that here; instead let me focus on how we can help our Earth in our own small ways. All of us are becoming aware of how quickly the population of the world is increasing and putting pressure on natural resources. Water tables are being depleted due to over-exploitation of groundwater reserves by uncontrolled digging of borewells. To help alleviate the situation or slow down the depletion process, let us try and collect rainwater and become independent to some extent while relieving the strain on natural resources. That is the least we can do at the micro level.
Water covers about three-fourths of the earth's surface, but only about 2 percent is fresh water. Of this small percentage, a large portion is trapped in the Polar region. In Asia, 86 percent of the fresh water is used for agriculture, 8 percent for industry and 6 percent for domestic purposes. Fresh water, once considered an inexhaustible resource, is now fast becoming a scarce commodity. The main source of fresh water is precipitation, in the form of rain or snow. When it rains, only a fraction of the water percolates and reaches aquifers; the majority of all rainwater drains away as run-off and goes unused into the ocean. Further, the lack of adequate storage facilities necessitates letting rainwater run into the sea to prevent breaching and flooding. The problem is compounded by a burgeoning and over-consumptive population, which has led to a spurt in bore-wells and also an increase in the depth of borewells. The two phenomena are manifestations of over-pumping of groundwater reserves. The unrestricted use of borewells threatens groundwater resources. The problem of groundwater depletion in cities and elsewhere can be best tackled by harnessing every drop of rainwater for the purpose of artificial recharge of the water table. There are methods for these, but we will not discuss them here.
Ever since my childhood, I've always wondered if rainwater could be stopped from flowing out and running away into the gutters. I used to do try to do it by collecting droplets from a window shelter into the very small tank in my little garden. I had no resources to improve my ideas. But the ideas were there and when I moved into our ancestral house, I was able to bring my ideas to fruition. I'm also one who advocates recycling of as many things as possible and so I had barrel, pipes and the likes that I had accumulated and/or bought. I collected water in a barrel using a simple sponge filter and it worked very well. This water was used for washing and for gardening. I was happy and wanted to do it on a larger scale and I eventually did, with very good results. The picture on the right shows the big tank. The picture on the left shows the system in our open yard, using a barrel. At a couple of other places with downspouts, I used crude methods to store rainwater--I did not want to waste any precious water!
At another downspout, where the water flow was not as heavy, I built a small tank to store it. This is how I did it very simply. The 'first filter' worked nicely, though it was not necessary for gardening purposes.
Having tasted success here, I wanted to implement my new project. The two tanks in the above photo were recently added to the portion of the house that my brother took as his share of the family division. My new project in the other portion of the house was more advanced; I decided to connect the inflow into the main water sump. So I got all my own plans ready after plenty of thought. Here is the basic system, ready for use.
If we have to divert and collect the rainwater in our main storage tank, a proper filter is a must because since we live in a city and impurities like fugitive dust from heavy traffic, leaves from nearby trees, bird droppings etc. are common. Earlier I used to have a sponge, and and a gravel gravity filter that worked well. But a good friend who is an authority and a great experimenter suggested using a filter and overflow method. I used 90 mm PVC pipes and a 30-gallon barrel for the filter. The downspout pipe is 75 mm. The outflow pipe should be equal or larger (not smaller). I have not used threading to fix pipes to barrel, just neat cuts (skill required!) and I had to fix the bottom drainage pipe (1 1/2 inch PVC) with threaded end cap, cut up to open.
This is the basic idea of the system I've now adapted.
The materials I have used are here include pipes, barrel, sponge, charcoal, sand, gravel (granite stone pieces).
Before water enters this system, it flows through what is called as 'first filter' that holds back heavier particles, thus making it easier for the main filter which holds back even minute particles of dust. Initially, the filter is arranged in such a way that water enters the barrel through the wire mesh to stop leaves and other thicker particles. In addition, I have used a broken bucket with hole in the bottom to hold a couple of sponge pieces to hold back even the smaller particles and placed it in such a way that the bucket can be remove to clean the sponges by beating and squeezing it out, flushing out the accumulation. This is a particular concern in my case because of the heavy traffic that creates fugitive dust--it is a large and unavoidable problem! So I have the extra step of the sponge-cleaning. In cleaner places, this may be unnecessary. Here is a photo.
Approximately 10 gallons of the first flow of rain washes out those partices and once that is flushed out, clear water continues to flow later. This filter is necessary for such a purpose.
This is the view of the flitering system. The outflow pipe is not yet connected to the sump, but I left it out to collect in a smaller barrel to see how clear the water comes out. When the gravel and sand, though washed before putting them in, I wanted a couple of rains to do the work in situ. It worked well and after I convinced myself about the clarity and the functioning of the experimental filter method, I connected it. Water fills in from below and after getting filtered, it overflows out.
I took this picture when it was actually raining, with an umbrella in one hand, camera in the other. Look at the water flowing out into the collection tray (I'll remove this eventually and connect it into the elbow.) I thought there might be some resistance in the center inflow pipe of the main filter as it has to fill up from the bottom. There will be, during heavy rains. But that was not a problem. Still, water gushed out of the output pipe, though there was some 'recoil' from the first filter. Notice that I've also put a layer of 2-inch thick sponge on which I've placed activated charcoal in a mosquito netting. This is to absorb smells when not in use. I've also put a wire mesh at the point of the outflow pipe to prevent any broken pieces escaping out into the sump (though there's little danger of that.)
For the drain mechanism to clean the filter materials by gravity, a threaded end PVC pipe is attached at the bottom of the barrel. Even that can be collected and put to the pots and plants. Water gushes out of this, cleaning most of the spaces between the gravel to make it ready for the next rain, so no clogging. That should be an added advantage in this method of filter.
This is what we get in the end: Clear water.
Presently we are using the water for washing and non-potable purposes (we use direct supply for this), but we intend to use it for that purpose also later on, once I get it checked. Those that have proper filters installed are drinking it too. Rainwater is pure water. It is potable and 'tastes' nice!
For washing clothes, it is good. For the plants, it is a boon.
Catch as much rooftop rainwater as you can, and purchase as large a storage tank as you can afford, and see how much you will enjoy. See how much the plants will enjoy--there should be no looking back. All materials are easy to get; just a bit of time and money are all that is required. Make hay while the sun shines! ☼