Discoloration Material Accumulation in Water Distribution Systems

Abstract

Despite a significant ongoing investment in asset renewal and rehabilitation and high compliance rates for drinking water quality standards, water companies continue to receive customer contacts relating to water quality, dominated by discoloration. This paper investigates the accumulation of material responsible for causing such discoloration in drinking water distribution systems from new field data. Engineering experience suggests that factors influencing this accumulation might include local pipe properties such as age, material, or diameter. On the basis of recent research, it also seems reasonable to expect hydraulic conditions and bulk water quality to be important. Results of extensive repeated flushing field trials in two representative distribution management areas (DMAs) over a two and a half year period are presented. Initial flushing suggested that the maximum thickness of discoloration material accumulated within the pipes was tentatively inversely proportional to the daily conditioning shear stress, in agreement with previous research, but independent of pipe material and/or diameter. An analysis of discoloration material from different strength layers, facilitated through stepped flushing, showed that the metal composition was uniform, and the process of accumulation simultaneously occurs across all strength characteristics. In plastic pipes, a limiting layer strength of