The quality of drinking water in the Netherlands meets high standards as is annually reported by the Ministry of Housing, Spatial Planning and the Environment (VROM)(Versteegh and Dik, 2006). Also the water companies themselves report in the voluntary Benchmark that water quality is one of the least discriminating factors as all the companies ‘comply generously’(VEWIN, 2004). Despite this reported high quality, water companies still report between 3000 and 6000 customer complaints about discolouration annually. The report on the Benchmark mentions that of all the parameters turbidity is causing most of the water quality failures. These figures are based on the data in the report system used to communicate the outcomes of the legal testing programme to the inspectorates (REWAB, 2004). The most common process associated with the phenomenon of discolouration is historically the corrosion of cast iron pipes as is suggested on the site of the Drinking Water Inspectorate in the UK (DWI, 2007). On many websites of Dutch water companies, however, particles originating during treatment are also identified as the source of deposits in the network. Many authors who studied the corrosion of cast iron in potable water systems conclude that this is a major cause of discolouration. (Smith et al., 1997; McNeill and Edwards, 2001). Recent studies (Prince et al., 2003) have suggested that more sources for particles besides from corrosion play a role in the discolouration problem. A large proportion of the customer contacts that drinking water supply companies across the world receive, stem from complaints on the occurrence of discoloured water in the drinking water distribution system (DWDS). Fig 1-1 shows a typical breakdown of customer contacts for a UK water company (Vreeburg and Boxall, 2007). Fig 1-2 shows some examples of discoloured water supplied to customers, that have led to the complaints.