Effect of temperature on the growth of opportunistic pathogens

In this study we investigate how the increase in the temperature of drinking water influences the growth of particular pathogens, known as opportunistic pathogens, in the drinking water distribution system. We introduce these opportunistic pathogens into a test set-up which simulates the normal situation in the distribution system, including varying water temperatures. This study’s findings will give us insight into the risks that arise when the temperature of the drinking water increases, reaching levels above 25°C. This knowledge will enable drinking water utilities to decide whether measures are needed to reduce these risks.

Rising temperatures of the drinking water in the distribution system are more frequent and the possible risks for the growth of opportunistic pathogens are increasing. The 25°C standard for drinking water is being exceeded more often in hot years, a situation that will only worsen as a consequence of climate change and the energy transition. This has meant that drinking water utilities are increasingly faced with questions about the effects of underground heating networks and other hotspots on the temperature of the drinking water. These factors lead to even higher temperatures in the drinking water system and increase the risk of public health problems presented by opportunistic pathogens.

The potential risk of higher temperatures

To achieve more understanding of the issue, drinking water utilities can study the influence of constant temperatures (15 to 30°C) on the growth of opportunistic pathogens under different conditions in the distribution system. Earlier studies have shown that increasing temperatures can lead to greater health risks, but these studies were conducted under optimal growth conditions. How increased temperatures under normal conditions in the system lead to growth of opportunistic pathogens is still unclear, however.

In order to investigate this, the present project examines the drinking water temperatures over a period of ten years, including variations during the course of a day and of seasons. This provides the basis to carry out experiments to determine the effects of temperature, pipe material, flow rate and drinking water type on the growth of five opportunistic pathogens. The analysis of these results using a risk analysis will produce greater insight into the possible implications for public health.

Project objective and impact

The ultimate objective of the project is to determine the influence of the heating up of drinking water on the growth of opportunistic pathogens under normal conditions in the distribution system. This will provide valuable information for drinking water utilities for the implementation of appropriate measures and to reduce the risk of the growth of opportunistic pathogens. The results can also be used in consultations with public authorities and other stakeholders, when discussing possible modifications to the legal standard for drinking water temperature.