The Effects of Climate Change on Microbial Ecology and Water Quality of Drinking Water Distribution Systems

Microorganisms inhabiting drinking water distribution systems (DWDS), particularly those forming biofilms attached to pipe surfaces, play a key role in determining the quality and safety of the final tap water supplied to consumers. Climate change is producing alterations in environmental conditions that can affect these systems and therefore its diverse microbiome, thus it may reduce the water quality and/or availability and accessibility. This may compromise the distribution of safe drinking water, resulting in detrimental consequences for public sanitation and human society. In this research the effect of different processes to which DWDS are susceptible as a result of climate change has been investigated. A unique full-scale DWDS facility at the University of Sheffield, which allow for the study of both biofilm and planktonic communities, was used to simulate realistic and controlled conditions. Advanced molecular techniques combined with the characterisation of key water physico-chemical parameters were applied to obtain a complete overview of what happened in the systems under different experimental conditions. The first part of this work evaluated the impacts of increasing temperature as a consequence of global warming. For this, biofilm was grown at different temperatures in the test loop facility. The study of biofilm mobilisation events showed that under high temperatures there was an increased risk of water discoloration and metals release into the bulk water. In addition, temperature was demonstrated to be a key factor shaping the microbiome of DWDS. The second part of the research studied the effect of temperature increase on biofilm control strategies: flushing of pipes followed by hyperchlorination, only flushing and without mechanical or chemical treatment. This study demonstrated that the increase of water discolouration at higher temperatures when the biofilm is mobilised depended on the biofilm control strategy applied. Furthermore, the management strategy applied was observed to be critical in determining biofilm community structure and composition, while planktonic communities were less affected by temperature increase and/or management strategy. Finally, experiments were carried out to understand how different intermittent water supply (IWS) times (6 hours, 48 hours and 6 days) impact on the microbiome of DWDS. This study evidenced that different IWS times affect in different way several physico-chemical parameters, including the discolouration response during the supply restarting. Similarity, microbiological analyses showed how biofilm experience structural and/or compositional changes during different IWS events and that planktonic communities were affected when supply was restarted. This research has improved the understanding of how different processes in relation to climate change can modify DWDS conditions and affect drinking water quality and safety. Results have provided new and valuable understanding that can be useful to adapt and mitigate the risks associated to climate change in DWDS and to protect the quality and safety of drinking water. In addition, it has highlighted the necessity of including biofilm monitoring and microbial culture-independent methods to generate more accurate microbial information and get an extensive view of what happens in the pipeline environment.