Yamuna & water
What is faecal coliform?
Faecal coliform is a count of bacteria that live in the gut of warm-blooded animals, reported as Most Probable Number per 100 millilitres of water. The bacteria counted are mostly harmless in themselves. They are measured because they are easy to find and they only get into water one way — so their presence means sewage is present, and whatever else was in that sewage is present too. India's bathing criterion is fewer than 2,500 MPN/100 mL.
An indicator, not the danger itself
Nobody is counting the thing that would make you ill. They are counting the thing that travels with it.
The pathogens that cause illness from contaminated water — the viruses and protozoa behind hepatitis, typhoid and most waterborne diarrhoea — are difficult, slow and expensive to test for individually, and there are many of them. Coliform bacteria are none of those things: they are abundant, cheap to culture and quick to count.
So the test is a proxy. Total coliforms occur widely in soil and vegetation, which makes them a weak signal. Faecal coliforms — the subset that grows at 44.5°C, dominated by E. coli — come overwhelmingly from the intestines of warm-blooded animals, so finding them in a river means gut contents reached that river. Faecal streptococci are counted alongside as a second, more persistent indicator.
The unit is not a headcount. MPN stands for Most Probable Number: the sample is diluted in a series of tubes, the pattern of which tubes grow is recorded, and the count is inferred statistically from that pattern. It is an estimate with confidence bounds, which is why the figures come in round-looking numbers rather than exact ones.
- MPN/100 mL
- Most Probable Number per 100 millilitres — a statistical estimate of bacterial density, not a direct count.
- Indicator organism
- Something measured because it travels with the hazard, not because it is the hazard.
- Faecal streptococci
- A second indicator, more persistent in water than coliforms, so a useful cross-check on how recent the contamination is.
What the law asks for, and what the river returns
The criterion is for outdoor bathing, notified under the Environment (Protection) Rules, 1986. The four readings below are CPCB's own published maxima for 2025.
Faecal coliform, bathing water
< 2500 MPN/100 mL
PWQC, Environment (Protection) Rules 1986
Faecal streptococci, bathing water
< 500 MPN/100 mL
PWQC, Environment (Protection) Rules 1986
Yamunotri, at source — maximum
2 MPN/100 mL
CPCB NWMP 2025
Palla, entering Delhi — maximum
2,200 MPN/100 mL
CPCB NWMP 2025
Nizamuddin — maximum
11,00,000 MPN/100 mL
CPCB NWMP 2025
Okhla, after the Shahdara drain — maximum
1,60,00,000 MPN/100 mL
CPCB NWMP 2025
The criterion is under 2,500. The last figure in that table is more than six thousand times it. Both numbers are published by the same agency in the same document.
The scale is the reason this measurement is worth understanding rather than just quoting. A pollutant at twice its limit and a pollutant at six thousand times its limit are not the same kind of finding, and no other reading on this site produces a ratio remotely like it.
How to read a coliform figure
It is a grab sample of a living population, and it behaves accordingly.
It moves fast. Bacterial counts respond to a rainfall event, a drain surging, or a hot week, within hours. A minimum and a maximum a year apart describe two different rivers, which is why CPCB publishes both rather than a mean.
It is not conservative. Unlike a metal or a salt, bacteria die off downstream — from sunlight, predation and time. A falling count between two stations can mean dilution, or it can mean distance. It does not on its own mean less sewage entered.
The criterion is for contact, not for drinking. Bathing water at under 2,500 MPN/100 mL is not water anybody should drink. Drinking-water standards for coliforms are effectively zero, and treatment is assumed.
What this number cannot tell you
- It cannot tell you which pathogens are present, or whether any are. It tells you sewage is, and that the risk is therefore not zero.
- It cannot distinguish human sewage from animal waste. Both are warm-blooded gut flora in this test.
- It cannot be compared across laboratories without care: the MPN method's dilution series sets the resolution, and different series give different upper reporting bounds.
- It says nothing about chemical contamination. A stretch can be low in coliforms and heavy in metals, and this number would not notice.
Where this comes from
Every figure above is read out of one of these, at the address printed beside it.
- Water quality data of river Yamuna, 2025 Central Pollution Control Board, National Water Quality Monitoring Programme · Every station figure above
- Primary Water Quality Criteria for bathing waters Central Pollution Control Board · The 2,500 and 500 MPN/100 mL criteria, and the designated-best-use classes
Reuse freely — CC BY 4.0. The grant covers this page. Each source above keeps its own terms, which is why every one of them is named.
Next
The reading this explains, the explanations next to it, and the one place to stand in it.
compared with other rivers? A national ranking of 47 rivers — and the coverage hole that stops it seeing the worst stretch of this one. Stand in it Yamuna Yatra The same river at two MPN and at sixteen million, in one continuous journey.