Summary: It is in years of plenty that we should stock up for times of shortage
Many people are moving into a problem solving mode but it needs institutional reinforcement to help achieve maximum benefits.
The major Public Sector undertaking has a very large campus and has a huge water demand. It draws water from the Bangalore Water Supply and Sewerage Board and pays a hefty Rs 60 per kilo-litre for the water. Being water smart, it has set-up a waste-water recycling unit and ensures that all waste-water is treated and reused for non-potable purpose particularly gardening .Lawns are extensive in the campus and is needed for dust suppression. The unit has also set up a huge lake to harvest run-off from its vast land. More than 170 million litres of storm-runoff is stored in this vast lake.
Their attention has turned to the large rooftop areas they have on campus. From 11,500 square metre of roof area, they simply connected the rainwater downpipes and brought it into a small 20,000 litre sump tank. From here they have put a pump to send the water directly into a much larger sump tank which takes water through a Reverse Osmosis unit. This R.O. water is needed for their manufacturing purpose. The investment they had to make was Rs 10 lakhs. Was the investment worth it?
The benefits translate as follows. They are likely to harvest 10 million litres of water annually. This will result in a savings of Rs 6 lakhs annually. The payback period for the investment is thus less than 2 years. There are other benefits. The embodied energy in alternate water, either from the BWSSB or bore-wells, is roughly 2 units of power per kilo-litre of water. The industry will therefore save nearly 20,000 units of power annually. This also translates as a savings in carbon emissions.
There are other benefits. The harvested rainwater is very soft with a Total Dissolved Solids of less than 50 ppm. This is likely to reduce further as the initial leaching of cement from the sump tank and the pipes become less. As against this the water they used from bore-wells had a TDS level of nearly 1000 ppm. The life of the membrane used for R.O. now increases. The reject water from the R.O. has fewer salts and can be recycled more easily than before.
The advantage is clear and it is likely that the industry will move quickly ahead to cover all roof-tops with rainwater harvesting systems. This means that over 100,000 square metres can be covered and over 100 million litres of rainwater harvested. No small feat for an industry located in a water scarce city.
A University: The University of Agriculture with a sprawling 1200 acres campus was once outside the city. Now it has become integral and falls within the Corporation Limits. Its water demand for agricultural crops is high. Most of the water comes from bore-wells. These are over exploited and many have gone dry. It has designed for itself a watershed based rainwater harvesting system. Thanks to a bountiful September rain a great amount of water has been collected and allowed to percolate into the ground. Many bore-wells have revived and are humming with water. The University is able to meet its water demands and students and Professors can continue to develop knowledge with experiments on the ground.
Groundwater banks are being created in the city by institutions that occupy large tracts of lands and have large rooftops. These efforts supplement the water delivery to the city and make the city water smart. Things have to be scaled up and more such institutions brought into the rainwater harvesting community. Further deeper understanding of how much water is actually recharged into the ground, what is a reasonable water demand to keep the groundwater banks humming for 2 to 3 years will ensure that the water shortfall in the city is overcome. Creative solutions using knowledge is the hall mark of the city and in this lies water wisdom.