This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
All of the following statements about purification of water are true except: 
Select and explain. 
A. Presence of Clostridial spores indicate recent contamination of water, B. Coliforms must not be detectable in any 100 ml sample of drinking water, C. Sodium thiosulphate is used to neutralize chlorine, D. Coliforms may be detected by multiple tube method & indole production
A: Presence of Clostridial spores indicate recent contamination of water
Answer: A: Presence of Clostridial spores indicate recent contamination of water 
Explanation: Ans is 'a' i.e., Presence of Clostridial spores indicate recent contamination of water Spores of Cl. perfrignence (in the absence of coliform group) indicate remote fecal contamination of water. o Total coliform bacteria must not be detectable in any 100 ml of sample. Sodium thiosulfate is used to dechlorinate tap water for aquariums or treat effluent from waste water treatments prior to release into rivers. It is also used to lower chlorine levels in swimming pools and spas following superchlorinat i on. Presumptive coliform count is done by multiple tube method and membrane filtration technique. After analysing presumptive coliform coutn. E coil count is cofirmed by other tests litre Eijkmant test and indole production.