Which indicator organism is used to assess faecal contamination of drinking water in India's water quality surveillance under NITI Aayog and BIS standards?

• A Total coliform count
• B Streptococcus faecalis
• C Clostridium perfringens (welchii)
• D Thermotolerant (faecal) coliforms / E. coli ✓

Explanation

Thermotolerant coliforms (faecal coliforms, predominantly E. coli) are the primary indicators of recent faecal contamination of drinking water. WHO guidelines and Indian standards (BIS IS 10500) specify that E. coli/thermotolerant coliforms must be absent in any 100 mL sample of drinking water. Total coliforms are a broader indicator including environmental non-faecal coliforms. Cl. perfringens indicates older contamination (can survive after coliforms die). E. faecalis is used as an indicator for well or treated water.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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