Which of the following is considered the common indicator organism of water pollution?

Escherichia coli is the common indicator organism whose presence signals faecal water pollution.

Amoeba causes disease but is not used as a routine pollution indicator.

Blue-green algae indicate nutrient overload rather than faecal contamination.

Dismissing all choices is wrong because E. coli is the standard indicator.

E. coli lives in the gut, so finding it in water points to sewage contamination.

Coliform counts are a basic test of drinking-water safety.