West Bengal | The Hooghly's googly

A Bengali version of the famous common man of cartoon strips could today be sketched in two frames—looking up from a newspaper in both, with a befuddled expression, the thought balloon filling up with exclamations and question marks. In one, a damning report says Bengal has left most of its sewage untreated despite spending hundreds of crores on cleaning the Ganga. The other is the complete opposite, not only saying pollution in the river has improved significantly but that West Bengal is the top performer in that entire chain of riparian states. Both are central reports.

So, the Hooghly has delivered a googly, and it helps to decode the two sides of the spin separately. The two reports turn out to be describing different things, albeit during substantially overlapping years. Read the nastier turn first. This spot of bad news comes from the Comptroller and Auditor General (CAG). Its performance audit, covering 2018-19 to 2022-23 and tabled in July 2026, examined how effectively Bengal was tackling water pollution.

The sewage treatment data... er, didn’t smell good. By March 2023, 41 sewage treatment plants (STPs) had been commissioned in 29 Ganga-front towns in Bengal under the Centre’s Namami Gange programme since 2014. But only 26 were working. Even these were treating just 232.5 million litres a day (mld) against their combined capacity of 383.8 mld. That is, only 61 per cent of capacity. Against the estimated sewage generation of 1,571.5 mld, that left a treatment gap of 1,339 mld—a frightening 85 per cent. The machinery was falling short at several levels: insufficient capacity, plants lying idle, and those willing to work getting less sewage than they could handle! Building a treatment plant, evidently, is not the same as getting sewage into it.

Now for the ball that went the other way, back in May. This was the National Mission for Clean Ganga’s account, which spoke of improved water quality in Bengal. The mission, which implements Namami Gange, cited a change in the Central Pollution Control Board (CPCB) ranking. Polluted river stretches are ranked for severity by their levels of Biochemical Oxygen Demand (BOD): the oxygen needed to break down biodegradable material in water. Higher readings indicate greater pollution; water with BOD over 3 milligram per litre is unsafe for even bathing.

Now, in the CPCB’s 2018 assessment, the Tribeni-to-Diamond Harbour stretch was Priority III. That’s BOD of 10-20 mg/l. In a 2025 assessment, the stretch from Baharampore to Diamond Harbour was placed in Priority V, or BOD 3.1-6. Much cleaner, though the measured stretch was longer. There was another catch in the dates. The “2025 assessment” does not describe water from 2025. It uses observations from 2022-2023. (The 2018 one: from 2016-2017.) So, both the BOD good news and the sewage bad news were, substantially, features of the same period.

The BOD classification doesn’t tell us everything about the water; a better reading can’t establish that the river meets all standards. And a sewage treatment audit answers a very different question anyway. A river can register lower concentrations of a certain pollutant and still have a flood of filth flowing into it.

The CPCB notes that pollution varies along a river, with things turning acute where its capacity to absorb pollution is overwhelmed. It collects several kinds of water quality data. This one is built around BOD, and doesn’t exactly say the water is inviting you for a swim.

There’s a further distinction between pollution concentration and pollution load. The former is how much pollutant is present in a litre of water; the latter is how much passes through over time—the amount of flowing water matters too. So the mission’s claim that the “actual pollution load has reduced considerably” does not hold too much water—or is at least not warranted by the BOD tick mark. What it is categorically not is an empirical claim that ‘x amount of pollution has stopped entering the river’.

WORK IN PROGRESS

None of this means the improvement is not real. Just that it does not wash away other sins. As of May 2026, Namami Gange had sanctioned 34 STPs worth Rs 5,028 crore in Bengal—Maheshtala, Jangipur, Chakdah, North Barrackpore just in 2025-26. Their combined capacity is pegged at 816 mld. It also reported 17 projects (558.5 mld) as complete. Work genuinely in progress, but they can’t have retrospectively improved water quality!

The CAG report is actually a useful guide about what to ask next: not just whether a plant has opened, but how much sewage reaches it, how much it actually treats and how okay the outgoing water is. Rather than be treated as contradictory, the two accounts can be profitably read together. Now we know not to blindly apply STP capacity as daily treatment achieved. Instead, we must always check the plumbing.

Thus dove-tailed, one day we’ll hopefully be able get a sangam of recent and current figures for comparison. If available today, we could have answered this: how much of the treatment gap documented in 2023 has since been closed, and with what results in the river? That’s a lot less cloudy water.