The 'free residual chlorine' in drinking water distribution system at consumer end should be maintained at:
Choose the correct answer
Zero (no chlorine required in distribution)
Minimum 0.2 mg/L free residual at consumer end for disinfection effectiveness
Always > 5 mg/L
Same as at treatment plant (no change allowed)
Correct Answer
B. Minimum 0.2 mg/L free residual at consumer end for disinfection effectiveness
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IS 10500 and WHO guidelines: free residual chlorine at consumer tap = minimum 0.2 mg/L and maximum 0.5 mg/L (to ensure disinfection without taste/odour complaints). At treatment plant: higher dose applied (1–2 mg/L) to account for demand and travel time in distribution. WHO permits up to 5 mg/L as a health-based value but taste limits to 0.6 mg/L.
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