Objective This study aimed to investigate the dynamic transformation between nitrite and ammonia in drinking water and to identify the key influencing factors. The findings are expected to provide a scientific basis for formulating active water quality risk control units, to promote the transformation of drinking water safety research from "meeting factory standards" to "achieving controllability at the tap", and to reduce the risk of nitrite exposure in drinking water.

Methods The experiment was designed to simulate real household water storage environments. Detection was conducted in accordance with the method for detecting nitrite (as N) and ammonia (as N) outlined in the Standard examination methods for drinking water-Part 5: Inorganic nonmetallic indices (GB/T 5750.5-2023). The evolution of these two nitrogen species was systematically monitored in five typical water sample types (tap water, boiled water, purified water, and samples spiked with nitrite or ammonia nitrogen) under both sealed and unsealed conditions over a storage period of 1 to 30 days.

Results The different storage methods had a significant effect on the nitritation reaction (F=9.889, P < 0.01). The maximum nitritation rate of ammonia in the open-storage group reached 1 105.96%/d, which was higher than that in the closed-storage group. The effect of free chlorine in the samples on the nitritation reaction was secondary (F=5.089, P < 0.01). The effect of initial sample pH on the nitritation rate (P>0.05) was not statistically significant.

Conclusion The transformation of the two nitrogen species during drinking water storage is governed by the combined effects of the dynamic balance of ammonia-oxidizing bacteria and dissolved oxygen levels. This study provides critical experimental evidence for supporting safe drinking water practices and the optimization of storage conditions.