A minimum concentration of how many mg/L must be measurable throughout the water system after leaving the chlorination station?

The correct minimum concentration of chlorine that must be measurable throughout the water system after leaving the chlorination station is 0.2 mg/L. This level is established to ensure effective disinfection of the water supply. Adequate chlorine residual is vital for maintaining bactericidal properties as the water moves through the distribution system, preventing the growth of pathogens and ensuring the safety of the drinking water.

Maintaining a chlorine concentration of at least 0.2 mg/L ensures that even at the farthest points in the system or during variations in water demand, there remains an effective concentration sufficient for disinfection purposes. The standard is in place to protect public health and ensure compliance with water quality regulations.

Achieving a higher concentration like 1 mg/L or lower values like 0.1 mg/L or 0.5 mg/L may not provide the same level of assurance that pathogens are effectively controlled throughout the water distribution system.