Which of the following is the largest source of water pollution in major…

Concept

The scale of a pollution source is judged by the total quantum — the volume and continuity — it contributes to a water body, not merely by how toxic what it releases is. Pollution-control assessments of Indian rivers classify pollutants by source — domestic sewage, industrial effluent, and agricultural run-off — and rank each source by the share of the total pollution load it contributes.

Application

Central and state pollution-control assessments — including analyses behind the National River Conservation Plan — consistently find that untreated municipal sewage, discharged continuously from towns and cities situated along the river course, forms roughly three-fourths of the point-source pollution load carried by major Indian rivers (that is, pollution entering at a discrete, identifiable outfall, as distinct from diffuse agricultural run-off). Most Indian towns and cities still lack adequate sewage-treatment capacity, so a very large volume of domestic wastewater enters rivers directly and year-round, making it the largest single contributor among all the source categories considered here.

Cross-check: why the other options fall short

• Agricultural run-off: concentrated in specific farming belts and tied to sowing and harvest seasons, so its national contribution to river pollution, while real, is far smaller in volume and continuity.

• Unregulated small-scale industrial effluent: can be highly toxic where it occurs, but such units are geographically clustered, so their aggregate discharge volume nationwide is much smaller than a continuous, year-round urban source.

• Religious practices such as idol immersion or ritual offerings: add a real but seasonal and localised load around specific festivals and pilgrimage sites, not a sustained, nationwide-scale contribution.

Because untreated sewage contributes the largest continuous volume among all these sources, it is the correct answer.