To investigate the effects of a corrosion inhibitor settling over an extended period, a two-part low-alloy steel pipe was taken from the drinking water network and installed in a test system. After an equilibration phase with inhibited water, the connected pipe sections were operated with inhibitor-free water for 600 days. During this time, stagnation tests were conducted to measure the increase in turbidity, oxygen consumption, and iron release. Corrosion rates and iron release rates were calculated from these parameters. Comparing the values at the beginning and end of the tests showed that the test pipe without the phosphate inhibitor did not exhibit a significant increase in the corrosion or iron release rate. The turbidity rates indicate that the legal limit for drinking water is reached after six hours of stagnation in the tested water. Under stable conditions, turbidity increased linearly over time, while oxygen consumption decreased linearly. Flushing significantly disturbed the corrosion system and increased the turbidity rate. The results obtained can be used to assess the risks associated with changes in water properties, in this study by discontinuing the addition of corrosion inhibitors, but also with modifications to water treatment such as aeration, softening, and desalination. In these cases, the impact on corrosive materials should be investigated beforehand. The results allow for the derivation of recommendations for optimizing the corrosion properties of the water or for implementing countermeasures in the supply network. The test procedure requires minimal personnel and financial resources, yet provides valuable insights into corrosion processes in the water-metal system.