Effect of water quality on red water release in iron drinking water distribution systems

Water quality deterioration in old distribution systems occur due to the release of corrosion products from the pipe surfaces. Cast iron and galvanized iron pipes are the major contributors of iron release in drinking water distribution systems. The surface films on the corrosion products can be disrupted due to changes in source water quality or flow. This decreases the acceptability of the water at the consumers tap.; Utilization of different source waters by blending is envisioned as a means of meeting increasing demands and reducing adverse environmental impacts on over-used single source waters. However, changes in the water quality could result in the release of surface films within the distribution system. This dissertation discusses an empirical modeling approach to evaluate the suitability of different blends based on the blend water quality. Significance testing of different water quality parameters indicates that alkalinity, chlorides, sulfates, sodium, dissolved oxygen, temperature and hydraulic retention time are the water quality parameters that have the most significant impact on color release in distribution systems. An empirical model that incorporates the effect of the significant water quality parameters was developed.; This research identifies alkalinity as the important controllable water quality parameter for red water mitigation. An alkalinity of above 80 mg/L as CaCO₃ is recommended.; However, alkalinity amendment by conventional bicarbonate salt addition would also lead to a corresponding increase in the sodium content of the water and thereby reducing the intended benefit. A modified form of the Larson Ratio is developed that will provide utilities with a quick estimate of the release problem associated with specific blends. This modified form is an improvement over the original form since it includes the effect of hydraulic retention time and temperature.; The empirical model and the modified Larson Ratio were verified by independent data. The verification was carried out to study the singular effects of alkalinity, sulfates and chlorides on color release.; The different pipe material often had conflicting water quality requirements. A multiobjective optimization technique was used to evaluate the optimal blends that minimized the release of iron, copper and lead simultaneously.