The impact of private networks on off-flavour episodes in tap water

Complaints registered by Veolia water agencies underlined the design and operating parameters in the private network can cause taste and odour (T&O) episodes. Three experiments were performed to elucidate the impact of the private network. Firstly, a lab-scale pilot study was designed involving four different pipes, consisting of copper, polyvinyl chloride, stainless steel and galvanized steel in which several residence times were simulated. The study was then conducted on a real private network. Finally, laboratory static experiments on tap seals were carried out. To evaluate T&O potential of drinking water samples, sensory analyses by a taste panel were performed. To detect and to quantify the molecules involved, stir bar sorptive extraction coupled with gas chromatography/mass spectrometry analyses was applied. The results showed that the residence time had a significant influence on the appearance of organic and metallic compounds. An audit of the private network identified two main critical points-corrosion and leaching-both of which are influenced by the hydraulic system. Finally, static experiments conducted on seals revealed a large quantity of polycyclic aromatic hydrocarbons leaching into water and a chemical or plastic taste according to the panel. These results suggest a huge potential impact of the private network on water quality if operating conditions are not optimal.