Environment › Pollution
Water pollution and river rejuvenation
Polluted rivers and lakes and what cleans them: sewage treatment and reuse, industrial effluent, contaminants in drinking water, and the programmes that rejuvenate rivers. Prelims has asked what biological oxygen demand measures and which pollutants are found in drinking water in parts of India.
UPSC has asked
- Prelims 2017: what biological oxygen demand is a standard criterion for
- Prelims 2013: pollutants found in drinking water in parts of India
Showing 1 of 6 subjects, those that changed from 16 to 31 July 2026.Show all
Polluted river stretches
Copy link to Polluted river stretchesPrelims
The Central Pollution Control Board counts a river stretch as polluted when its biochemical oxygen demand exceeds 3 mg a litre, and publishes the count periodically as the national measure of river pollution.
What changed
21 Jul 2026New subject
- The Central Pollution Control Board now counts 296 polluted river stretches, down from 351 in 2018.
The Hindu, 21 Jul 2026
Also filed elsewhere
- Fluorosis · on Non communicable diseases, nutrition and food safety
Fluorosis is not a poisoning that arrives from a factory: the fluoride is in the rock the groundwater passes through, so a village can drink it for years with nothing having gone wrong upstream.