The time water can remain in storage before re-chlorination is required depends on reservoir conditions, climate, and the type of disinfectant used. In most cases, chlorine or chloramine residuals are expected to remain effective for a few days up to about a week. However, in hot climates or in uncovered reservoirs exposed to sunlight and organic matter, disinfectant levels may drop more quickly, sometimes within 24 to 48 hours.
Chloramine generally lasts longer than free chlorine, which is why some utilities prefer it for systems with large reservoirs or long distribution pipelines. Even so, both forms of disinfectant gradually dissipate over time, and operators must regularly test water to ensure residuals stay within safe limits.
