New Delhi, Dec. 10 -- The National Green Tribunal (NGT) has raised fresh concerns over possible contamination of a key stormwater drain that feeds Delhi's drinking water supply, after being informed that sewage from Haryana's Diversion Drain No. 6 (DD-6) is spilling into Diversion Drain No. 8 (DD-8). The tribunal has now asked the Haryana government to clarify whether DD-6 is, in fact, a stormwater drain and whether it is being permanently tapped and diverted to a sewage treatment plant (STP).

The issue is significant because DD-8 is a freshwater drain that carries water eventually treated and supplied to Delhi, making any mixing of untreated waste a serious environmental and public-health risk.

The NGT had first taken suo motu cognisan...