Spores of Cl. perfrignence (in the absence of coliform group) indicate remote fecal contamination of water. Total coliform bacteria must not be detectable in any 100 ml of sample. Sodium thiosulphate 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 superchlorination. Presumptive coliform count is done by multiple tube method and membrane filtration technique. After analysing presumptive coliform coutn, E coli count is confirmed by other tests litre Eijkmant test and indole production.