Water Pollution — Revision Notes

⚡ 30-Second Revision

Checked 18 October 2026.
DO = oxygen present; BOD = biological oxygen demand.
CPCB A: DO ≥6, BOD ≤2 mg/L; B: ≥5, ≤3.
A still requires disinfection.
Two passing parameters do not prove full compliance or potability.

2-Minute Revision

Start with the use and contaminant. Organic matter can raise BOD and reduce available oxygen; nutrient enrichment can lead to growth followed by oxygen-consuming respiration and decay. Low BOD does not exclude microbial or toxic hazards. Match the sample, test conditions and complete parameter set to the designated-use criteria before making a safety claim.

5-Minute Revision

For DO 5.5 and BOD 2.5 mg/L, compare the two stated CPCB thresholds for Classes A and B. Explain why full classification remains unresolved. Draw the eutrophication pathway and identify where oxygen demand rises. Finish by proposing separate checks for sewer collection, treatment performance and receiving-water outcomes.

Vyyuha Quick Recall

USE: Use defines the standard; Stock of oxygen differs from demand; Evidence must cover the required parameters.