Dive into Success: Conquer the 2026 Water Treatment Grade 4 Exam and Make Waves!

The minimum disinfection residual level that must be maintained in water served to a population over 3,300 for up to 4 hours is indeed 0.2 mg/L. This level is crucial for ensuring that the water remains safe for consumption by effectively inactivating pathogens and preventing the regrowth of microorganisms as the water travels through the distribution system.

Maintaining a residual disinfectant in the water helps safeguard public health by providing a consistent defense against any potential contamination that may occur after the initial disinfection process. The specific level of 0.2 mg/L has been established considering factors such as the size of the population served, the length of time water may be held in the system before use, and the potential for fluctuations in water quality. This requirement helps water utilities ensure they deliver sufficiently treated water to avoid outbreaks of waterborne diseases.

Other levels listed, such as 0.1 mg/L, 0.5 mg/L, and 1.0 mg/L, do not meet the minimum requirement for maintaining effective disinfection during the specified conditions for larger populations.