To address the growing water needs in Mumbai, the Brihanmumbai Municipal Corporation (BMC) is set to construct an 8.7 km-long water conveyance tunnel. This tunnel will connect the upcoming sewage treatment plant (STP) in Dharavi with BMC’s water filtration plant in Bhandup.
Water conveyance tunnels are designed to transport large volumes of water efficiently. Unlike conventional pipelines, these tunnels have a larger diameter, enabling them to move greater quantities of water at maximum speed. Civic body officers have stated that the water transported through the tunnel will be tertiary treated, which means it will be treated to a level suitable for non-potable uses. Additionally, the water can undergo further treatment at the Bhandup plant to make it safe for drinking, after which it can be supplied to households and commercial establishments.
Why a water conveyance tunnel?
Mumbai requires 4,200 million litres of water daily (MLD), while civic authorities currently supply approximately 3,850 MLD, leaving a deficit of around 10 per cent. Of the total 3,850 MLD consumed daily, around 3,040 MLD, or 78.96 per cent, ends up as wastewater or sewage. Currently, this entire volume flows into the Arabian Sea and nearby creeks without adequate treatment.
Therefore, to combat this issue, the BMC proposed to set up seven state-of-the-art sewage treatment plants at Mumbai’s Worli, Dharavi, Ghatkopar, Bhandup, Bandra, Versova, and Malad for Rs 27,000 crore in 2022. All seven STPs will have a collective capacity to treat 2,464 MLD of water daily, with the Dharavi plant capable of recycling 418 MLD of water each day. Initially, 50 per cent of this, or 209 MLD, will be treated to the tertiary level for non-potable use.
“After the tertiary treatment of water is completed, it will be transferred to the Bhandup plant. From there, it can either be filtered and transferred to the city for drinking purposes or sold to private stakeholders for revenue generation,” an officer explained.
Potential non-potable uses of this recycled water include landscaping, gardening, and road washing. Various private stakeholders, including power supply operators and petroleum supply chains, have already expressed interest in BMC in acquiring this water for their operations.
Future tunnel developments
The water conveyance tunnel received Coastal Regulation Zone (CRZ) clearance from the state government last week, and construction is expected to begin soon. The tunnel will measure 8.48 km in length, with a diameter of 2.7 metres.
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While the BMC initially aims to supply 209 MLD, the tunnel’s total capacity will allow for the transport of up to 418 MLD of water. The construction will involve excavating hillocks from beneath the ground, with an average depth of 150 metres and a peak depth of 155 metres around Ghatkopar. The project’s cost is estimated to be Rs 3,000 crore. In the long term, the BMC plans to develop a series of water supply tunnels connecting each STP in Bhandup, Ghatkopar, and Dharavi to the filtration plant in Bhandup. The total capacity of these three tunnels will reach 970 MLD.
In the long run, BMC plans to develop a series of water supply tunnels connecting each STP in Bhandup, Ghatkopar, and Dharavi to the filtration plant in Bhandup. The total capacity of these three tunnels will stand at 970 MLD.
“As of today, Mumbai has a demand of 4,250 MLD of water, against which BMC can supply only 3,850 MLD, resulting in a deficit of 400 MLD and at least 15 per cent shortage of water, especially during peak summer periods, owing to the delayed monsoon. Therefore, the 970 MLD quota of water, which will be earmarked for tertiary treatment after the seven STPs become operational, will more than double Mumbai’s overall water deficit,” the officer added.
Civic body officials acknowledged that many people have concerns regarding the purity of STP water. Therefore, before using tertiary water for drinking purposes, suggestions and objections from the public will be gathered through a formal process.
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“In countries like Singapore, tertiary water is mixed with raw water in reservoirs and subsequently supplied to households after filtration. We aim to implement similar measures here, which is why the capacity at the filtration complex is being enhanced,” the officer noted.
