Microbiological indicators of the quality of river water, used for drinking water supply

Pathogenic microorganisms are a common component of surface water reaching rivers along with sewage. If present in small quantities, they are not a threat to the health and life of humans, but in larger quantities can be a pathogenic factor causing much discomfort. The amount of pathogenic bacteria in river waters varies depending on various factors such as the size of the stream, the season, water level, degree of eutrophication of the watercourse and its tributaries, or geographical area through which the river fl ows and the ability of a watercourse to self-clean. In view of the risks that may be caused by microorganisms pathogenic to humans and animals, a constant monitoring of their quantity in surface waters has been carried out. As follows from studies conducted for the past several years (1999-2010), the number of coliforms and thermo-tolerant coliforms in Wisłoka River water near Mielec showed a downward trend, while that of fecal enterococci (Enterococcus faecalis) a growing tendency. At that time there was no evidence of Salmonella. In almost the whole study period, pollution of human origin exerted a major impact on the sanitary conditions of tested water. Only in 2006 were they of the zoonotic nature. Analyzed sanitation parameters of surface water in the Wisłoka River collected in a water intake point for the city of Mielec showed high variability, depending on the season and water pH. Coliform bacteria showed the highest number at the lowest pH (≤7.0). There was very high, positive correlation (rx,y>0.7) between the number of microorganisms and selected physicochemical indicators of water quality. Count of coliform bacteria and thermo-tolerant coliform type increased along with the increase in the value of electrolytic conductivity. The largest correlation (rx,y = 0.85) was recorded between the number of fecal enterococci and the level of BOD5 indicator.