India, July 16 -- A new survey of the Yamuna has revealed an alarming truth: the Najafgarh drain, long known to be the river's biggest polluter, is pumping nearly twice the estimated volume of untreated sewage into the Yamuna. And a significant chunk of this pollution isn't even Delhi's doing - it originates in Gurugram.

The revelation is part of an ongoing analysis by the Delhi government to assess untreated sewage flow into the Yamuna from the city's 22 major drains. According to Delhi water minister Parvesh Verma, fresh findings indicate that the Najafgarh drain alone now carries around 800 million gallons per day (MGD) of sewage into the river-up from previous estimates of 450 MGD.

Even more striking is that nearly 250 MGD of that w...