Susmita Sengupta is a senior programme manager with the Water Programme at the Centre for Science and Environment (CSE), a Delhi-based environmental research and advocacy group. A geologist by training, she brings over 20 years of experience in water management and sanitation, having advised key ministries and non-profits in India and abroad.
Her policy expertise has shaped major national initiatives, including the Jal Jeevan Mission and the National Mission for Clean Ganga. In an email interview with The Statesman’s Muskan Bhatia, Sengupta discussed Yamuna pollution, the shortcomings in current clean-up efforts, and what it will take to revive the river in Delhi.
Q. Is the Yamuna clean before it enters Delhi? What changes once it flows into the city?
A. The river has ‘life’ at the time it enters Delhi at Palla and Wazirabad, but by the time it reaches the next monitoring station at ISBT, it is effectively ‘dead’. This analogy draws from a key physical parameter — dissolved oxygen (DO) — which determines whether a water body can support aquatic life or not. When DO levels are sufficient, the river can sustain plants, fish, and other organisms, symbolizing that the river is alive. Conversely, when DO levels drop too low to support these forms of life, the river is considered dead. To assess pollution levels in the Yamuna within Delhi, the Delhi Pollution Control Committee (DPCC) monitors eight key points, from where the river enters the city at Palla to where it exits near the Okhla Barrage. DPCC’s data shows that dissolved oxygen levels at Palla and Wazirabad meet the acceptable standard of 5 mg/litre; below this, the water is unfit for bathing purposes. But by the time the river reaches ISBT, DO levels fall to zero; in other words, the river is now officially without life. Pollution levels in the Delhi stretch of the Yamuna remain a major concern. Although only 22 km of the river flows through the city, this segment contributes nearly 80 per cent of the total pollution load. The situation remains dire even during the monsoon when pollution levels typically improve — yet last year, DPCC reported nil DO levels. The trend has shown little improvement. As of last month, DO levels at Palla — where the river enters Delhi — stood at 9.8 mg/litre, well above the acceptable standard. However, midstream and downstream sections continue to report zero DO, despite sewage treatment plants (STPs) operating at nearly 100 per cent capacity.
Q. What are the main sources of pollution in the Yamuna within Delhi? Where do they come from?
A. The primary source of pollution in Delhi’s stretch of the Yamuna is domestic sewage. While industrial waste does play a role in degrading the river’s health, the scale of untreated human waste entering the river is far greater. According to the 2019 Action Plan by the River Rejuvenation Committee for the Yamuna, nearly 50 per cent of Delhi’s population still lives in areas without access to a proper sewage network. In these neighbourhoods, there is no system in place to intercept or treat waste. The untreated waste flows directly into open drains, which eventually empty into the Yamuna. This problem is reflected in key pollution indicators monitored by government agencies. One of them, Biochemical Oxygen Demand (BOD) measures the amount of oxygen required to break down organic matter such as sewage. Ideally, BOD levels should be below 3 mg/litre, but recent data has shown levels 40 to 50 times higher, a sign of severe organic pollution. Faecal Coliform (FC) counts, which reveal the extent of bacterial contamination from human and animal waste, are also alarmingly high. During dry spells, some downstream locations have recorded over 2 lakh colony-forming units per 100 millilitre, far exceeding safe limits.
Q. Despite crores of rupees spent in recent years, the Yamuna remains polluted. Why haven’t these efforts worked?
A. The current strategy under the Yamuna Action Plan focuses on multiple fronts to tackle the pollution in the river. These include constructing more STPs to intercept and treat domestic wastewater, improving the quality of treatment to ensure cleaner discharge into the river, and building interceptor sewers to tap existing drains and prevent the mixing of sewage with stormwater drains that carry rainwater and urban runoff. The plan also involves laying sewage pipelines in unauthorised colonies and ensuring that industrial waste is treated at designated common effluent treatment plants (CETPs) before discharge. While these are commendable steps in the right direction, there are some gaps that remain, leaving the river still heavily polluted. Our analysis has shown that estimates of 100 per cent wastewater treatment in Delhi may be misleading as there is no reliable estimate of total wastewater generation. As a rule of thumb, about 80 per cent of the total water used turns into wastewater. However, accurately estimating Delhi’s wastewater generation remains a challenge due to major data gaps. Population figures — a key factor in calculating wastewater — are unavailable, and estimates based on water supply are unreliable. Nearly 40- 50 per cent of the city’s water is lost in distribution, yet this unaccounted loss is still reflected in official wastewater estimates. To bridge the gap between supply and demand, many areas rely on water tankers, which also remain outside official records. Adding to the inaccuracy, millions of residents live in unauthorised colonies without proper sewage connections. In these areas, waste is often collected through septic tanks and desludging tankers, which frequently discharge untreated waste directly into drains or the Yamuna. Additionally, sewage from unauthorised and informal settlements often goes unaccounted for since it isn’t officially intercepted.
Q. What, in your view, needs to change in how we are approaching Yamuna cleaning?
A. CSE’s action agenda for cleaning the Yamuna in Delhi highlights the urgent need to prioritise faecal sludge management – the safe collection, transport, treatment, and disposal of sewage waste from areas not connected to the city’s central sewer network. This is especially critical given that, according to the 2019 River Rejuvenation Committee report, nearly 50 per cent of Delhi’s population lives in settlements without proper sewage infrastructure. In such areas, waste is typically collected in septic tanks or holding tanks, and often ends up being emptied by private desludging operators into drains or water bodies without treatment. While the current Yamuna Action Plan includes provisions for faecal sludge management, it remains a low priority in implementation. As of February 2025, only 160 private desludging vehicles were officially registered in Delhi and are being tracked by Delhi Jal Board officials. However, many more such trucks operate across the city without any formal registration, tracking, or regulation, leaving the final disposal site of the collected sludge unknown. This lack of oversight raises serious concerns about illegal dumping and river pollution. Even more concerning, only 1 per cent of the wastewater classified as faecal sludge was actually treated. CSE has called for immediate steps to scale up efforts, including registering and tracking desludging vehicles using GPS, ensuring the waste reaches authorised treatment plants, and promoting the safe reuse of treated sludge, such as for agriculture or landscaping, wherever feasible. Additionally, the mixing of treated and untreated wastewater must be prevented. Since many STPs are located far from the river, their treated effluent is discharged into nearby drains, which often also carry untreated sewage from unsewered areas, defeating the purpose of treatment. Thus, the river stays polluted. We recommend prioritising the reuse of treated wastewater, particularly for horticulture and agriculture, instead of releasing it into drains where it mixes with untreated sewage. Currently, only 10-14 per cent of treated wastewater is reused in Delhi, highlighting a missed opportunity. Each STP must have a clear plan not only for treatment but also for safe discharge and reuse. To make this effective, CSE suggests that stringent discharge standards should apply only when treated water is released directly into the river. For land-based reuse, where treated wastewater can help improve soil fertility, the standards can be tailored accordingly.