Residents from Andheri to Malabar Hill will have improved water supply from 2013 as the pipeline supplying drinking water to them will not be prone to pilferage and leakage.

The civic body completed a major step towards building the Marol Maroshi-Ruparel College underground water tunnel on February 18 when it finished drilling and boring a 12-km-long tunnel 70 metres below the ground, which is equivalent to the height of a 22storey building.

The tunnel will become operational by September 2013.

Supplying water to the city through underground tunnels instead of pipelines on the surface dramatically reduces the risk of water pilferage, contamination and leakage. Water theft is a major problem in Mumbai, with nearly 20% to 25% of water supplied disappearing in this manner.

The tunnel will connect to the Dr E Moses Road tunnel, which is already operational and supplies water to Malabar Hill.

It is expected to improve water supply to Vakola, Mahim, Dadar and other parts of the island city, which currently get water from the Brihanmumbai Municipal Corporation (BMC) through 80-year-old surface pipes that are susceptible to bursts and pilferage.

The tunnel is being constructed under the Centrefunded Jawaharlal Nehru National Urban Renewal Mission (JNNURM) and is part of the project to improve the distribution of drinking water from the Bhandup water treatment plant to the western suburbs and south-west of the city.

Now that the boring and tunneling are over, the lining of the tunnel -a process to prevent any seepage -will begin.

The BMC has given the Rs415-crore contract to build the 12-km tunnel, which starts from Marol Maroshi in Andheri to Ruparel college in Matunga to the Hindustan Construction Company, which has constructed the Bandra-Worli sea link.

“The tunnel can't be tampered with as happens with surface pipes, so there are fewer chances of leakages and pilferage,“ said Kapil Raman, project director, HCC.