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Project Overview

Introduction

In the UK we take for granted the security of our water supply, not just the certainty of turning on our taps and being able to watch the water flowing, but also knowing that the water is clean, clear and safe to drink.  Water companies are legally responsible for the quality of drinking water that issues from our taps, with the need to meet drinking water quality standards (EU Drinking Water Directive 98/83/EC).  Even though water companies have exceedingly high compliance rates (>90%), there are a number of failures whose cause is unknown.  One potential source of such failures is the contamination of drinking water due to the ingress of pollutants into the distribution system from the surrounding soil and water. However the actual risk posed by this mechanism is entirely unknown.

PIpe Leak
Broken sewerage pipe above a leak in a water main. 
(Karim, M, M. Abbaszadegan, and M.W. LeChevallier. Potential for pathogen intrusion
during pressure transients,  JAWWA, 2001)

Leakage is an accepted feature of distribution systems. Such leakage is considered to occur outwards due to the pressure differential between the water in the pipe and the lower pressure in the surrounding ground. However, distribution networks are dynamic systems with frequent changes in hydraulic conditions. Such changes induce transients in the form of pressure waves that move throughout the network. Transient events may induce negative pressures over relatively short durations. Hence, the pressure of the water outside the pipe may briefly be greater than the pressure inside the pipe and there is potential for ingress. Such ingress volumes are likely to be small but may contain harmful contaminants. The smallest traces of certain contaminants may cause a water quality failure whilst others may promote bacterial growth and adverse chemical reaction, ultimately impacting on public health.

The potential for ingress is dependent on a number of factors, including the occurrence, frequency, duration and magnitude of transients within systems, the effective size and geometry of the apertures and the ground conditions in the immediate vicinity of the pipe. The consequence of ingress is a function of where it occurs, the character and concentration of the contaminant, the population exposed and the disinfection residual of the water within the pipes.

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Maintained and updated by Richard Collins and Sam Fox, June 2015