Drinking water testings—evaluation of long-term data of temperature and microbiological parameters | Trinkwasserbefunde – Auswertung langjähriger Daten der Trinkwassertemperatur und mikrobiologischer Parameter mit Indikatorfunktion

The provision of microbiologically safe drinking water is one of the main tasks of drinking water supply. Regular drinking water tests are an essential guarantee for the compliance with hygienic requirements and can provide information on long-term developments and general correlations between parameters. Within the scope of a project to determine the temperature influence in the drinking water supply, authorities from Lower Austria made an anonymized selection of their database available for evaluation. Accordingly, the main focus is on the analysis of temperature measurements in connection with the microbiological parameters CFU at 22 °C, 37 °C and the coliform bacteria. In addition, most of the evaluations were carried out for the drinking water distribution system.With regard to long-term trends, the data show an annual increase of the measured temperature at sampling points within in the distribution network of about 0.064 °C. Periods with very high values of water temperature were recorded in August 2015 and 2018 as every third sample in the distribution network exceeded 20 °C. Mainly decreasing trends were found for the microbiological parameters. For CFU at 22 °C the decrease is about 0.5 CFU/ml per year. Despite these contrary trends, it cannot be assumed that the increase in temperature will not have a (negative) impact on the microbiological situation. In a regression analysis, the influence of temperature was found to be significant for the CFU at 37 °C. Thus, an increase in temperature from 15 °C to 20 °C increases the probability of values >20 CFU/ml from 0.077 to 0.109. This finding can be considered plausible from a microbiological point of view, although the temperature here could only indicate longer network residence times. The influence of other at least equally important factors, such as the organic content of the water, can’t be represented as precisely due to a lack of available data.