Water conservation through rainwater harvesting
RV College of Engineering, Bangalore, has over the past year collected and used close to 17 lakh litres of rainwater. This is the result of a project undertaken alongwith Bangalore based Biome Environmental, which is engaged in ecological architecture and responsible water practices, to store the rooftop rainwater and use it in day to day activities including drinking.
The only source of water for RV College of Engineering (RVCE) was borewells. This was not found sustainable. In general, groundwater has many quality issues – it is a little too hard which means there are excess minerals especially in the form of carbonates. In order to make the groundwater suitable for drinking, the water from the borewells had to be passed through a six stage purification process which included “softening” as well as reverse osmosis. Since both the issues of quantity and quality had to be addressed, the college decided to go for rainwater harvesting taking help from Biome Environmental. The project involved tapping rainwater from three large rooftops and directing it to an underground tank.
The project was funded by the KPMG Foundation. Biome had previously implemented another project funded by them at the Accept Society – a HIV centre located in Bangalore.
In the Accept project, there was a total roof area of 760sqm which included sloping roofs, from where rainwater was collected and stored.
Being a college campus, RVCE has plenty of large rooftop areas from where rainwater could be harvested. After studying the overall site plan and the lay out of the campus, Biome zeroed in on three buildings. The main challenge was in terms of the storage structure. This was going to be a big underground tank and as such we needed a fairly large area to locate it. The buildings chosen have a combined roof area of 3000sqm and in Bangalore context this means that during a single shower the campus can collect upto 80,000 litres of rainwater, going upto 1.6 lakh in the event of a heavy downpour. Seen in an annual context, the college will potentially collect 20 lakh litres of rain during the year. The annual rainfall we have assumed in case of RVCE is 724mm which is lesser than the 970mm one would assume for Bangalore city. The reason for this is that the college itself is not really located within the city but on the ourskirts in an area called Kengeri. As has been observed round the world, the city centre actually gets more rain than the outlying areas. One reason for this is the “heat island effect” or the excess build up of heat due to the roads and dense buildings in the city.
From the college side, this project was supported by Professor Shivkumar, Head of the Civil Engineering Department. Since 2004, he has been attending conferences and trying to learn more about rainwater harvesting. The college had earlier done a borewell recharge project on the campus.
Having large rooftops brought its own challenge in terms of filtration. During peak rainfall, there would be enormous volumes of water flowing through the pipes necessiating filters which could do the job quickly and efficiently and send the water into the sump tank without any inordinate delay. For this Biome designed “above ground” filters with the largest of these being 2,000 litres capacity with 1000 litres volume for First Rain Separation and 1000 litres for filtration. Basically, with any rainfall, it is the first 1mm of rain to be precise, which contains the maximum impurities and the First Rain Separator is meant to take care of this.
There are three separate filters for each of the rooftops leading directly to the sump tank which is of 1.28 lakh litres capacity. Essentially, a single rain of 50mm can fill the tank and just a few days after the completion of the project, this is what happened. On the day that the system was to be inaugurated, the sump tank was almost full of rainwater.
In addition to the storage tank we also made a “recharge well” with the intention of seeping the rainwater into the aquifer or sub surface storage. In the event of a heavy downpour there is every possibility that the sump will overflow and rather than just allowing the extra water to flow into the nearest drains, we felt it would be better to direct it to the ground.
The project was completed in March 2010 and in the first 8-9 months since its inception, the college estimated that it had collected 17 lakh litres. A sizable quantity of about two to three lakhs litres of water has gone in for groundwater recharge. What is important is that the water is pure and doesn’t require as much treatment to make it fit for consumption. The “softening” process, for instance, is being bypassed in the case of rainwater.
Collecting rainwater has resulted in conservation of groundwater and also savings in terms of electricity. The college is in the process of conducting a study to estimate the real benefits from rainwater harvesting.