Which of the following is not true about water quality estimation –
Option 'a'

Coliform organism → Most commonly used bacteriological indicates
Faecal streptococci → Recent faecal pollution of water.
Spores of Cl. perfringence (in the absence of coliform group) → Remote faecal contamination of water.

About other options
Option 'b. & d'

Total coliform bacteria must not be detectable in any 100 ml of sample.
But, In case of large supplies, where sufficient samples are examined, coliform bacteria must not be present in 95% of samples taken throughout any 12 months period → Not more than 5% samples should have Coliforms.

Option 'c'

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 superchlorination.
Clostridium spores indicate recent contamination
Not more than 5% samples should have coliforms
Sodium thiosulfate added to neutralize chlorine
Coliforms must not be detectable in 100ml sample