Common indicator organism of water pollution is :-

Escherichia coli (a coliform bacterium) lives normally in the intestine of humans and other warm-blooded animals and is passed out in faeces in huge numbers.
Its presence in water shows that the water is contaminated with sewage (faecal matter) and may contain disease-causing organisms. So the coliform count (E. coli count) is the standard test of the quality of drinking water.
Eichhornia (water hyacinth) and Lemna grow abundantly in nutrient-rich (eutrophic) water but are not the standard indicator. Entamoeba is a pathogen, not a routine indicator.
So the common indicator organism of water pollution is Escherichia coli.