Water supply to several pockets in south Calcutta has been erratic since January-end, with officials blaming it on the receding water level in the Hooghly and the absence of a large reservoir in Garden Reach water works.
The affected stretches are Garfa, Behala, Tollygunge, Jadavpur and Santoshpur.
Unlike Palta water works, the Garden Reach facility, which supplies filtered surface water to these pockets, do not have any sedimentation tank to hold buffer stock.
The Palta reservoir can store up to two days unfiltered water, ensuring uninterrupted supply to a large part of the city between Cossipore and Bhowanipore even when the pumps are out of order.
Officials said a similar reservoir was badly needed in Garden Reach, as the pumps there frequently break down in the winter and summer when the water level in the Hooghly falls drastically.
But there is no way we can build a similar reservoir in Garden Reach or in the vicinity because of lack of space, said an official.
Explaining the reason for the Garden Reach pumps frequently going out of order, civic chief engineer Bibhas Maity said the water level often dropped below the mouth of the intake pipes during high tide, resulting in the giants pumps sucking in air.
Repairing the pumps takes a long time. And if by the time the process is over low tide sets in, we have to wait for another seven-eight hours for the water to rise above the mouth of the pipes and start operations, said an official.
In the past 25 years, the water level during high tide has gone down by two feet, he added.
Till the 1970s, the water level used to go down to 19 feet and 10 feet below the road level during low and high tides, respectively. Since 1980, civic engineers pointed out, the water level has receded up to 21 feet and 12 feet below the road level during low and high tides.
The period between the first week of February and the first week of March is particularly troublesome as the water level frequently falls below the suction level.