Why the Yamuna Foams Before Chhath, and How Much of It Is Our Own Sewage

On 24 October, white foam was back on the Yamuna below the Okhla barrage, drifting toward Kalindi Kunj. Three weeks later, from 13 to 16 November, lakhs of people will stand in this river at sunrise and sunset for Chhath Puja.

The foam is not a mystery and it is not only Delhi's problem. It is made from what goes down our drains, including drains that start in Gurugram. This post explains what the foam is, what the government's own September 2026 readings show, and what a housing society, school or office in Delhi NCR can actually do about it.

What the foam is made of

The foam is mostly surfactants: the chemicals in detergent, shampoo and soap that make water froth. They arrive in sewage along with phosphates from detergents, ammonia and decaying organic matter. When that water drops over the gates at the Okhla barrage, the churning whips it into foam the way a washing machine does.

In late October a Delhi minister said there was "no foam anywhere" in the river's 52 km through the city and blamed turbulence at the Uttar Pradesh border. The Delhi Pollution Control Committee (DPCC) later said the foam is surfactant foam, which does not form from turbulence alone. Turbulence only shows what is already dissolved in the water.

It appears every year at this time for a simple reason. During the monsoon, floods dilute the sewage. By October the flow drops, the dilution is gone and the same sewage shows up at full strength.

What DPCC's September 2026 readings show

DPCC samples the Yamuna at 23 points in Delhi every month. The key measure is BOD (biochemical oxygen demand): the more sewage in the water, the higher the BOD. Water fit for outdoor bathing should have a BOD of 3 mg/L or less and dissolved oxygen (DO) of at least 5 mg/L.

Only Palla met the BOD standard. At all 23 points, faecal coliform was above the bathing limit of 500 MPN/100 ml; at Asgarpur it was 38 times the limit, and there was no dissolved oxygen left at all. A river with no oxygen cannot break down what is poured into it.

Where the sewage comes from

Delhi produces about 3,600 million litres of wastewater a day and has treatment capacity for about 3,000, and the plants do not always run at capacity. The gap, plus sewage from colonies that are not on a sewer line, goes into drains that empty into the river. The largest is the Najafgarh drain, which joins the Yamuna near Signature Bridge, just above the ISBT reading in the table. It carries wastewater from parts of Haryana as well as Delhi, and Gurugram's storm drains flow toward it.

That matters for anyone living in Gurugram. A society whose sewage treatment plant (STP) is switched off at night to save power, or whose treated water is quietly let into the storm drain because nobody uses it, adds to the foam at Kalindi Kunj. So do the colonies with no STP at all. Gurugram's own groundwater is already pumped at nearly twice the rate it is recharged (see the district page), so treated water that could be reused for flushing and gardens is water the city cannot afford to throw away.

What a housing society, school or office can do

1. Run the STP you already have, all day. An STP that runs only when the inspector comes treats nothing. Check the treated water monthly against the BOD in your consent to operate.
2. Size it properly. Many older plants were sized for half the people now living there. The STP capacity calculator works out the size you need in KLD from the number of flats and people.
3. Reuse the treated water. Piping it back for flushing, gardens and car washing cuts fresh water use by a third or more and keeps it out of the drain. Our sewage treatment plant service designs and builds the plant and the reuse lines.
4. Keep sewage and rainwater apart. Sewage in a stormwater drain goes straight to the river; rainwater in a sewer overloads the STP in the monsoon. Rainwater belongs in a recharge pit, as the recharge pit guide shows.
5. Use phosphate-free detergents in common laundries, hostels and canteens, and ask your housekeeping contractor to do the same.

A revived village pond with a reed bed at its inlet also cleans greywater before it reaches a drain. Gurugram has lost many of its ponds; the Gurugram ponds page shows how many, and pond rejuvenation in Gurugram explains how we bring them back.

If you are going to the ghats for Chhath

• Use an artificial pond or a cleaner ghat where your area has one.
• Do not swallow river water or let children play in the foam.
• Rinse off with clean water as soon as you can, and see a doctor if a rash or itching does not settle in a day.

For CSR teams

Sewage treatment, reuse and pond revival are among the most measurable water projects a company can fund: litres treated per day and litres of fresh water saved are easy to report. CSR water conservation explains how we deliver them. For a site visit or a review of an existing STP, send us the details. If your society uses a borewell, the quality of what comes out of it matters as much; see is your borewell water safe to drink.

Sources

• DPCC readings, sewage figures and Chhath dates as reported by ETV Bharat, 3 November 2026.
• The minister's statement and DPCC's response: Karmactive, 27 October 2026.
• Foam near Okhla and Kalindi Kunj on 24 October: The Hans India.