The city is losing as much as 40 million gallons per day (MGD) of water due to the ill-maintenance of the Ranney wells on the Yamuna floodplains.
This amounts to 150 litres of water for 25 lakh people daily.
The Delhi Jal Board (DJB) maintains 21 Ranney wells across the length of the Yamuna.
During an on-going study about tapping Yamuna floodplains as a source for additional raw water, however, field experts noticed that several of these wells were working at less than half of their capacity.
Many of the wells were choked with silt and few were dysfunctional due to salinity.
One Ranney well can tap up to 2MGD water everyday, experts point out. Thus, 20-21 Ranney wells can yield 40 MGD water at full capacity.
Named after its inventor, Leo Ranney, the Ranney well taps shallow aquifers and sub-surface water from floodplains. DJB currently has the capacity to supply 845 MGD water per day obtained through various sources.
"It was found that most of the Ranney wells are working at only 25-30% of their capacity. Malfunctioning of the Ranney wells reduce the amount of water drawn and lead to a shortage in water supply," said Shashank Shekhar from Delhi University's department of geology. Shekhar was also part of the study carried out by WAPCOS, a government consultancy firm.
"We were told about such complaints. We need to find out if these wells require redevelopment and whether the equipment is working at full efficiency or not," said RK Garg, member, DJB. "I have sought a report from the officers concerned," Garg added.
The WAPCOS study, however, suggests the use of a non-invasive approach, such as tubewells as against Ranney wells.
"The study suggests that Ranney wells lead to a point stress in the system (of underground and sub-surface water). So, to reduce the burden and avoid environmental problems, it is advisable to go for tubewells spread over an area," added Shekhar.