Beginning Monday 9.30 am, filtered water supply to different parts of Calcutta, Salt Lake and Cossipore will be severely affected for two weeks.

While Monday’s dry spell, caused by the shutdown of the Palta and Garden Reach waterworks, will last 20 hours and be confined to Calcutta, the second round will last a fortnight, and supply is likely to fall by 40 million gallons to facilitate the commissioning of water treatment plants.

But there is good news, too. After two weeks, Calcuttans will enjoy the benefit of an extra daily supply of 20 million gallons.

After shutting down for 20 hours, filtered water supply will resume at 7 am on Tuesday. “The temporary shutdown of the waterworks for a few hours is essential for long-term augmentation of the city’s water supply after two weeks,” said mayor Subrata Mukherjee.

According to mayoral council member (water supply) Sovan Chatterjee, though water supply will resume from Tuesday morning, there will continue to be a shortfall of 40 million gallons in the supply from the Tallah-Palta network for about two weeks.

Municipal commissioner Debashis Som had asked chief engineer (water supply) Dibyendu Roychaudhury to take steps so that the shortfall in the water supply is minimised. Thereafter, steps have been taken to generate more filtered water by stretching the capacity of the old water treatment plants at Palta.

Besides, supply of filtered water to Salt Lake and Cossipore will be curtailed to some extent to tackle the situation. Salt Lake gets 10 million gallons of filtered water daily from the Calcutta Municipal Corporation and Cossipore receives 18 hours of continuous filtered water supply.

Engineers in the water supply department, however, think the actual shortage of filtered water will not be more than 15 million gallons.

Waterworks will close down to connect the newly-commissioned 60-million-gallons-a-day treatment plant with the city’s main supply artery, snapping off the old pipeline under the Gariahat flyover, and to connect the newly-laid pipeline between Behala and Bansdroni with the water supply main from the Garden Reach waterworks.

The city’s filtered water needs are met by two units: the Tallah-Palta network of the Calcutta Municipal Corporation and the Garden Reach waterworks of the Central Municipal Water and Sanitation Authority. While Palta delivers 200 million gallons to Calcutta and Salt Lake daily, the daily supply from Garden Reach is 70 million gallons.