Civic agencies face the daily challenge of supplying drinking water to 95 lakh people. To tackle this, two geologists have done a study and come out with some interesting figures and solution.
The study says that about 22 lakh Bangaloreans face acute water shortage. The solution lies in preventing the surface run-off getting wasted in the drain along with sewage load. Water conserved thus could meet the requirement of about 24 lakh Bangaloreans.
Another solution lies in treating the sewage load at tertiary level so that such treated water is made available for domestic and drinking purposes of 25 lakh residents.
Facts first: In their study on ‘Resource availability and status of water supply to Bangalore’, former senior geologist KC Subhash Chandra and senior geologist GV Hegde with the state department of mines and geology found that of the 800 sq km BBMP area, nearly 560 sq km had concrete structures and asphalted roads. The remaining 240 sq km was open.
The normal annual rainfall in the city is 830 mm. Of 66,400 hectare metre (ham) of rainwater received annually, 17,040 ham (25.66 %) goes as surface run-off, 2,125 ham as recharge to groundwater body and the balance 47,235 ham (71.13 %) as evapo-transpiration losses.
The population within BBMP limits is expected to cross 95 lakh by 2020.
“Considering the BWSSB norm of designed supply of 140 litre of water per head per day for drinking and other domestic needs, the water requirement for the city population of 95 lakh will be 133 ham per day or about 48,600 ham per year.
“Of 37,375 ham per year tapped from distant rivers with 30% loss, the supply remained about 24,923 ham per year,” he said.
There had been an estimated average withdrawal of 12,450 ham per year of groundwater to meet the deficit in water supply. Thus, there has been a shortage in supply of 11,225 ham per year. This means nearly 22 lakh Bangaloreans face acute water shortage.
“There are 3.12 lakh borewells in the city apart from unreported ones. While groundwater recharge from various sources is 3,290 ham per year, the withdrawal of 12,450 ham per year amounts to 378% or nearly 4 times more than the annual ground water recharge,” Chandra said.
People have resorted to indiscriminate drilling of borewells to depths beyond 250 m.
Save water
Suggesting steps to counter the shortage in supply, Chandra said a surface run-off of 17,040 ham per year is wasted by getting drained along with the sewage water load. If this water is conserved, it can meet the requirement of about 24 lakh Bangaloreans.
Similarly, if the total sewage load of 26,316 ham per year generated in the city is treated and brought to the safe standard of domestic and drinking water usage and 70% of such water is made available, it can serve the demand of the city population of another 26 lakh, he said.
Thus, the rainwater run-off and the treated sewage water together can serve the water requirement of about 50 lakh people or 53% of the city population.
Strict enforcement of water-related rules and Acts shall help in better management of water resources in a mega city like Bangalore, he said.
