CBET-EPSRC: Characterizing the effects of supply hours and pressure of intermittent piped water supplies on water quality

Lead Research Organisation: University of Sheffield
Department Name: Civil and Structural Engineering

Abstract

This project will study the effect that regular loss of pressure in water distribution systems has on water quality through a collaboration between the University of Massachusetts Amherst in the US and the University of Sheffield in the UK. The research will produce a better understanding of the effect of intermittently operated piped water systems on water quality and the results can be used to develop strategies to reduce the spread of waterborne diseases.
The influence of momentary loss of pressure due to pressure transients in continuous distribution systems has been relatively well-studied. However, while there is evidence of contamination in intermittent systems and corresponding adverse health impacts, there have been few studies exploring the mechanisms affecting water quality in chronically intermittent systems. The practice of intermittent water supply (IWS) can exacerbate risks to water quality that are observed in continuous supplies by introducing atypical hydraulic conditions imposed by the four phases of an IWS supply cycle. First, when the supply is off in the distribution network, pipes are at low or atmospheric pressure and may be partially or fully empty, thereby permitting entry of contaminants through leaks from adjacent groundwater or sewage depending on the conditions. Second, the water supply is then turned on to the pipes, filling the pipes with water and possibly mobilising contaminants accumulated at the pipe wall. Third, the pipes provide pressurized supply for a limited period of time, thereby transporting the mobilised material. Finally, supply is turned off again, leaving water in pipes to drain through household connections and leaks. While these hydraulic conditions can affect many aspects of the biological, chemical, and physical quality of the water, one of the most significant health concerns is the potential for intermittency to introduce waterborne pathogens into these distribution systems and to influence their transport, survival, and growth.

Our previous work hypothesized that the main mechanisms affecting this microbiological water quality in an intermittent water supply are: 1) mobilisation of contaminants from the pipe wall interface and corresponding interactions with the bulk supply (specifically biofilms, loose deposits, and microbial growth); and 2) ingress of contamination from outside the pipe when pressure is low, through either intrusion or backflow. However, while results from our field studies of intermittently supplied networks at scale suggest these two mechanisms are important contributors to contamination as demonstrated by the presence of fecal-indicator bacteria, the relative importance of these two mechanisms has not been studied under controlled conditions. Gaining a more fundamental understanding of how interruptions of supply affect the microbiology of pipes will allow for development of strategies to control potential health risks in both chronically intermittent networks and during interruptions to otherwise continuous supplies, such as after main breaks and for seasonal water systems.

The research will use the internationally-unique 600m long temperature-controlled, real-scale pipe loop facility at the University of Sheffield alongside pilot scale test rigs to be constructed at the University of Massachusetts. The three hydraulically isolated loops in the Sheffield facility will be operated with different supply regimes (continuous supply, 12 hours of supply every day, and 12 hours of supply twice per week) to establish baseline quality parameters, determine the presence, composition, and function of microbial communities, study the biofilm structure and composition, and investigate the survival and growth of indicators of pathogens. The data generated from these experiments will be used to develop a quantitative microbial risk assessment model to evaluate the impact of varying hours of supply on the potential risk of waterborne disease.

Planned Impact

Water distribution systems are a critical control point for maintaining the quality of drinking water. In high-income countries which normally have continuously pressurised water supply, the important role of distribution systems in protecting public health has been re-enforced after extreme failures, for example in Flint, Michigan, which led to an outbreak of Legionella pneumophila, or during natural disasters such as hurricanes, which have led to interruptions to supply and contamination of distribution systems and source waters by pathogen-containing floodwater. In low- and middle-income countries, access to piped water has been increasing; however, rapid urbanisation and a changing climate are threatening the reliability of these systems, often leading to reduced quality of service in the form of sustained interruptions to supply. The contribution of this proposed work will be to elucidate the fundamental mechanisms by which interruptions to supply influence the microbial ecology and behaviour of pathogens in biofilms and in the bulk phase of the water supply. Ultimately, the goal of this research is to improve our ability to control waterborne disease in water supplies used for drinking by identifying the most appropriate methods for control and operation of water distribution systems under intermittent supply. The proposed research will open a new field of enquiry within water quality in distribution systems, which until now has focused almost exclusively on continuous systems, to positively impact society in high as well as low- and middle-income countries by leading to practicable strategies to improve water quality and therefore reduce risks to health.

In addition, this joint US-UK project will train researchers to engage in international collaborations and global workforces, particularly related to meeting the sustainable development goals. The US Accreditation Board for Engineering and Technology, Inc (ABET) introduced "professional skills" into its criteria for engineering education, which includes "the broad education necessary to understand the impact of engineering solutions in a global, economic, environmental, and societal context", and the US National Academies of Science, Engineering, and Medicine vision of an engineer in 2020 also emphasises the importance of developing professional and teamwork skills as well as understanding engineering in a global context. Engineering UK estimates that an additional 79,000 engineering graduates per year, with deep and broad understandings of global issues as part of their hybrid skill sets, will be needed in the UK through 2024.

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