The rapid industrial, economic and social development in Chennai has resulted in a sharp increase in water demand, and placed a great strain on the limited sources in Chennai. The leakages for a minimum pressure of 10 m in the distribution system of CMWSSB during 1989-90 were very high, ranging between 45-50%. The board intended to curtail these leakages so that the existing water resources are utilized to the fullest potential.
The board has implemented a phased (5 phases) programme of UFW with World Bank assistance, to bring down leakages and UFW. Since the city's water supply is intermittent, a new innovative technology of pressuring the sub-district to 10m head using mobile water tankers was adopted to measure the leakage level under Phase I. The study revealed that 77% of the leakages detected were at the point of HSCs (due to non existence of ferrules) with leakage rates being 265 l/c/hr in CI mains and 391 l/c/hr in PVC mains at 10 m pressure. Under phase II, rectification programme was conducted, and ferrule replacement and other leak repairs were done, which resulted in reducing the leakage levels to 76 l/c/hr in CI mains and 391 l/c/hr in PVC mains at 10m pressure.

As it was difficult and time consuming to identify micro leaks at HSCs, the board conducted a water mains survey under phase III, IV and V, and replaced the corroded mains by taking a sample of the mains of 1m length at each street or 150m intervals. All house service lines from ferrule point to the meter chamber in Chennai city were renewed using MDPE pipes provided with poly propylene stop-taps. Subsequently, a sub-district was isolated for a minimum period of 1 hour and leakage level was measured at 10 m pressure. Leaks identified using electronic equipments such as leak noise correlator and sounding rods were rectified, and the average leakage achieved was 2.47 l/c/hr.

Based on the encouraging results, the board proposed to continue to renew the left out 30,000 HSCs with MDPE pipes. To measure bulk flows to and from major distribution stations, the board installed 48 bulk meters. The board had also opted to implement customer metering, and entrusted M/s GdE, UK, to recommend a way forward for complete domestic metering. As part of this, a study conducted in pilot area reveals that if all customer connections in CMWSSB are metered, the revenue of the board would go up by 564%. The study also recommended the implementation of phased metering programme.
After completion of the programme, the level of UFW was brought down from 50% to 17%.

The cost of water saved per annum works out to Rs. 19.41 crores @ Rs. 15 per KL at a supply pressure of 3m. The water loss reduction strategies and leak management adopted by the board are suitable for any water utility of any size in India. The conventional leak detection techniques adopted are suitable generally for 24 hours supply such as net night flow etc. However, the model developed by the board by shortening of the district and pressuring the system externally (by mobile/static tankers) worked effectively for detecting leaks in the intermittent supply.

For further details, contact:
Mr. Shiv Das Meena, IAS
Managing Director
CMWSSB