Public water-supply disinfection: which method is considered the best routine process for distribution systems?

Introduction / Context:
Municipal water-treatment trains include a final disinfection step to inactivate pathogens and to maintain a residual within the distribution network. The question asks for the best routine process for public water supplies.

Given Data / Assumptions:

• Centralized, continuous treatment for a public distribution system.
• Need for a persistent disinfectant residual in the pipe network.

Concept / Approach:
Chlorination (free chlorine or chloramine) is widely used because it provides both primary disinfection and a lasting residual to protect against regrowth and intrusion. Boiling is effective at point-of-use but impractical for systems. Lime adjusts pH/softening but is not a disinfectant. Ozone and UV are excellent primary disinfectants but do not provide a lasting residual; often they are paired with a small chlorine dose downstream.

Step-by-Step Solution:

Verification / Alternative check:
Standards and design manuals specify chlorine residual maintenance (free or combined) throughout the network for regulatory compliance.

Why Other Options Are Wrong:

• Boiling (a) is point-of-use emergency treatment, not system-wide.
• Lime (c) is for softening/pH, not disinfection.
• Ozonation (d) and UV (e) lack distribution residual and are usually coupled with chlorine/chloramine downstream.

Common Pitfalls:
Assuming strongest primary disinfectant equals best system method; network protection needs residual.

Final Answer:
Chlorination