The E. coli standard for piped water supply treated and distributed (not at source) as per Indian standards is:
- A < 1 E. coli per 100 mL
- B Zero E. coli per 100 mL in treated piped supply ✓
- C < 10 E. coli per 100 mL
- D < 50 E. coli per 100 mL — acceptable for rural supply
Correct answer: B. Zero E. coli per 100 mL in treated piped supply
Explanation
For treated piped drinking water supplies, the standard (BIS and WHO) requires zero E. coli (thermotolerant coliforms) per 100 mL. This is the absolute limit — any E. coli positivity indicates faecal contamination requiring investigation and remediation. For untreated source water (river, well), E. coli < 10/100 mL is considered of 'low risk', 10–100/100 mL is intermediate, and > 100/100 mL is high risk. The zero-tolerance standard applies only to treated/chlorinated supplies.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.