Asset deterioration and discolouration in water distribution systems P.S. Husband*, J.B. Boxall Pennine Water Group, Department of Civil and Structural Engineering, University of Sheffield, Mappin street, Sheffield S1 3JD, United Kingdom article info Article history: Received 18 June 2010 Received in revised form 4 August 2010 Accepted 10 August 2010 Available online 17 August 2010 Keywords: Hydraulics Shear stress Cohesive material Regeneration Asset deterioration abstract Water Distribution Systems function to supply treated water safe for human consumption and complying with increasingly stringent quality regulations. Considered primarily an aesthetic issue, discolouration is the largest cause of customer dissatisfaction associated with distribution system water quality. Pro-active measures to prevent discolouration are sought yet network processes remain insufficiently understood to fully justify and optimise capital or operational strategies to manage discolouration risk. Results are presented from a comprehensive fieldwork programme in UK water distribu- tion networks that have determined asset deterioration with respect to discolouration. This is achieved by quantification of material accumulating as cohesive layers on pipe surfaces that when mobilised are acknowledged as the primary cause of discolouration. It is shown that these material layers develop ubiquitously with defined layer strength characteristics and at a consistent and repeatable rate dependant on water quality. For UK networks iron concentration in the bulk water is shown as a potential indicator of dete- rioration rate. With material layer development rates determined, management decisions that balance discolouration risk and expenditure to maintain water quality integrity can be justified. In particular the balance between capital investment such as improving water treatment output or pipe renewal and operational expenditure such as the frequency of network maintenance through flushing may be judged. While the rate of development is shown to be a function of water quality, the magnitude (peak or average turbidity) of discolouration incidents is shown to be dominated by hydraulic conditions. From this it can be proposed that network hydraulic management, such as regular periodic ‘stressing’, is a potential strategy in reducing discolouration risk. The ultimate application of this is the hydraulic design of self-cleaning networks to maintain discolouration risk below accept- able levels. ª 2010 Elsevier Ltd. All rights reserved. 1. Introduction Discolouration remains the single largest water quality issue facing water companies worldwide. Of the 154,985 customer complaints about drinking water quality in 2007 for England and Wales, 124,671 (80%) were about discoloured water. Yet with a 99.96% compliance with the European Drinking Water Directive, the overall result for England and Wales is compa- rable with the best reported in Europe. In 2007, 33% of all incidents investigated by the UK Drinking Water Inspectorate * Corresponding author. Tel.: þ44 114 2225416; fax: þ44 114 2225700. E-mail addresses: s.husband@sheffield.ac.uk (P.S. Husband), j.b.Boxall@sheffield.ac.uk (J.B. Boxall). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/watres water research 45 (2011) 113 e124 0043-1354/$ e see front matter ª 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2010.08.021