Primary source: from contact with human excreta or animal waste. Typical examples include E. coli and other bacteria, viruses, protozoa-type microorganisms

Most likely: in groundwater when well is made near latrines or where there is human and/or animal contact with the water; in surface waters if stream or lake has significant inflow from urban runoff or untreated sewage

Effect: Diverse. Diarrhea and typhoid fever are typical examples.

WHO guidelines for drinking water quality