What is the purpose of maintaining a residual disinfectant in the distribution system?

• A. To kill all minerals in water.
• B. To continue inactivating pathogens and protect against microbial growth between treatment and consumption.
• C. To reduce the pH to acidic levels.
• D. To color the water.

Answer: (B)

The main idea is to keep a disinfectant in the distribution system so disinfection stays active as water moves from treatment to customers. After treatment, the disinfectant is gradually consumed by reactions with organic matter, by microbes in biofilms, and by any minor intrusions or contamination that can occur in pipes, tanks, or fittings. Maintaining a residual means there’s still enough disinfectant left to inactivate any pathogens that might enter or begin to grow, helping to prevent microbial growth throughout the system until the water is used.

This residual also serves as a practical safety check. If the disinfectant level drops too low, operators can respond by flushing lines or adjusting treatment to restore protection before water reaches consumers.

The other options don’t fit because residual disinfectants aren’t used to remove minerals, they aren’t primarily added to lower pH, and they aren’t intended to color the water.