It is in years of plenty that we should stock up for times of shortage, advises S. Vishwanath
This 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 purposes, particularly gardening .Lawns are extensive on 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.
Now its attention has turned to the large rooftop areas on campus. From 11,500 sq. m of roof area, the authorities simply connected the rainwater downpipes to a 20,000-litre sump. From here a pump sends the water into a much larger sump which takes water through a Reverse Osmosis unit. This R.O. water is needed for manufacturing purpose. The investment made for this water treatment was Rs. 10 lakh. Was the investment worth it?
The benefits translate as follows. The PSU is likely to harvest 10 million litres of water annually. This will result in a savings of Rs. 6 lakh annually. The payback period for the investment is thus less than two years. There are other benefits.
The embodied energy in alternative water, either from the BWSSB or borewells, 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.
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 and the pipes become less. As against this the water used from borewells 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 sq. m can be covered and over 100 million litres of rainwater harvested. No small feat for an industry located in a water-scarce city.
The University of Agriculture Sciences with a sprawling 1200-acre 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 borewells. These are overexploited 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 borewells 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, and what is a reasonable water demand to keep the groundwater banks humming for two to three years will ensure that the water shortfall in the city is overcome. Creative solutions using knowledge is the hallmark of the city and in this lies water wisdom.