Data on water quality of the river Yamuna and of Delhi's sewage treatment plants (STPs), common effluent treatment plants (CETPs) and drains - mandated to be posted at least once a month - has not been updated for over three months.
The Delhi Pollution Control Committee (DPCC), mandated by the National Green Tribunal (NGT) to upload monthly reports, last shared water quality data for STPs, CETPs, and drains in September. The latest available report on the DPCC website for the Yamuna and major drains dates back to October.
Officials from the DPCC and the Delhi government did not respond to queries on whether sampling has been discontinued or why the data has not been published.
The absence of current data is particularly concerning as the lean winter season - characterised by reduced water flow and lower temperatures - typically leads to a deterioration in river water quality, including increased frothing.
In 2019, NGT directed DPCC to maintain and disclose monthly water quality data to ensure accountability. Regular reports had been available since January 2013 for the Yamuna and from 2019 for drains and treatment plants.
Water quality testing involves collecting samples from eight locations along the Yamuna's course through Delhi - from Palla to Asgarpur - measuring parameters such as Biological Oxygen Demand (BOD), dissolved oxygen, chemical oxygen demand, pH, and fecal coliform. Similar tests are conducted for over 25 major drains across the city.
The last available report, dated October 25, showed alarming readings. BOD levels peaked at 25 mg/l - over eight times the safe limit of 3 mg/l - despite increased water releases from the Hathnikund barrage ahead of Chhath Puja. Fecal coliform levels reached 8,000 MPN/100 ml against a standard of 2,500. An earlier October report recorded even worse conditions, with BOD at 33 mg/l and fecal coliform at 21,000 MPN.
For context, during the same period last December, BOD levels had soared to 70 mg/l, with fecal coliform reaching an alarming 8.4 million MPN/100 ml.
Experts stress that transparency is critical, especially now, to assess pollution levels when the river is most vulnerable. "It is unclear whether samples were not lifted in November and December, or that it is not being shared. We see a deterioration in the water quality post-monsoon as the flow in the river reduces. We have also been seeing defoamers being sprayed across the river since October, but its impact on the water quality is not known," said Pankaj Kumar, a Yamuna activist also known as Earth Warrior on X.
Activists and researchers warn that the data gap undermines efforts to track river health. "We know the water quality worsens significantly in winter. Typically one can compare it to last year to see whether there is an improvement or not. Missing data sets a poor example for river governance," said Bhim Singh Rawat, a Yamuna activist, and member of the South Asia Network on Dams, Rivers and People (SANDRP).