Pilot studies on discolouration loose deposits' build-up

Tap water discolouration occurs due to resuspension of loose deposits (LD) that accumulate in drinking water distribution systems. Strategies for discolouration control involve network pipe cleaning and replacement of cast-iron pipes. However, the sole application of such measures is not generally effective. Therefore, a deeper understanding on processes associated with LD origin and development is required. Transparent (but covered) test rig pipes (Ø = 23 mm) continuously supplied with drinking water at steady flow through mode (7–9 months) were used to investigate LD build-up under laminar flow (0.2–4.1 cm/s) conditions. Rather than continuously and homogeneously, LD developed as spots, and predominantly at the pipes' bottom. Results suggested that particle attachment may be added to settling as a LD build-up process. This is consistent with LD cohesive–adhesive properties, as shown by LD repose angle tests, as well as to the occurrence of flocculent extracellular polymeric substances-EPS in LD.