All of the following statements about purification of water are true, EXCEPT:
The presence of spores of Clostridium perfringens in a natural water suggests that faecal contamination has occured, and their presence in the absence of the coliform group, suggests that faecal contamination has occured at some remote time. Its presence in filtered supplies may indicate deficiency in filtration practice. These spores are capable of surviving in water for a longer time and usually resist chlorination. Ref: Park's Textbook of Preventive and Social Medicine By K. Park, 19th Edition, Pages 58-1; Two's Water Supply By Don D. Ratnayaka, 6th Edition, Pages 241-2, 247
Level of residual chlorine in water should be 0.5 mg / L
Presence of Clostridium spores indicates recent contamination
Coliforms must not be detectable in any 100 ml sample of drinking water
Coliforms may be detected by multiple tube method and indole production