Abstract: Making use of alternative sources of water (e.g. desalinated water, reclaimed water) and long distance water diversion are possible methods to solve water shortage problems. However, source water switching might cause undesirable water quality changes at consumer taps resulted from destabilization of corrosion scales in existing drinking water distribution systems (DWDS). In the present study, cast iron pipes historically transporting groundwater were harvested from three sites of an existing distribution system of a northern city in China, and pipe-loop simulation distribution systems were established to investigate the effects of different alkaline chemicals on iron release inhibition performance. For better comparison, the sulfate concentration of feed water was manipulated to obtain relatively high iron release. The results showed that:1) The iron release decreased significantly with alkalinity supplementation (through NaHCO₃ addition) in the range of 94-251 mg/L (as CaCO₃) and could ensure the total iron concentration met the GB 5749-2006 Standards for Drinking Water Quality (<0.30 mg/L). 2) When water pH was elevated by addition of NaOH in the range of 7.83-9.01, the iron release was promoted to some extent instead of inhibition; while when the pH was elevated by adding Ca(OH)₂, the iron release decreased obviously, but the total iron concentration was always higher than 0.30 mg/L. 3) Under the condition of low sulfate concentration of feed water, the iron release did not increase when NaHCO₃ and Ca(OH)₂ addition discontinued, but under high sulfate condition, iron release could increase again with the termination of alkalinity and pH adjustments.