The article is focused on the description of problems that can be caused by increased temperature of drinking water in public drinking water distribution system (DWDS). Increased water temperature is an actual issue that the water industry has had to address in recent years, particularly as a result of the ongoing climate change. In recent years, long periods with high air temperatures have been more frequent than before. High air temperatures warm soil horizons and this results in an undesirable increase in drinking water temperature in water mains. Temperature is a physical, sensible indicator of water quality that affects a variety of chemical, biological, and microbiological processes in water. Therefore, the optimum temperature range of 8–12 ° C, which is to be achieved by the drinking water in the DWDS, is set by Decree of Ministry of Health of the Czech Republic no. 252/2004 Coll. Long-term high level of water temperature also contributes, among other things, to the development of the microbiological component of water in the DWDS and to the deterioration of organoleptic characteristic such as unpleasant odour or taste. The paper summarizes the technical regulations that are designed to provide the recommended water temperature in the DWDS, as well as the specific consequences and operating faults that may occur when water temperature is outside the optimum range of values. In view of the conclusions of available studies focused on predicting the future climate in the Czech Republic, it can be assumed that in the near future more frequent problems of operation can be expected in water supply systems due to unacceptable drinking water temperature. Above all, there will be water quality disturbances involving temporary deterioration of organoleptic, biological and microbiological indicators.
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