Monochloramines for Water Disinfection

Monochloramine (NH₂Cl) is widely used as a secondary disinfectant in water systems due to its stability and prolonged effectiveness. Here’s a comprehensive overview of its benefits, limitations, and comparisons with other disinfectants.

Benefits of Monochloramine

  1. Stability and Longevity: Monochloramine remains stable in water over extended periods, making it highly effective in maintaining disinfectant levels across large and complex plumbing systems, such as those in large factories, office buildings, and correctional facilities. This stability is particularly beneficial for ensuring residual disinfectant levels even in hot water systems.
  2. Lower Disinfection Byproducts: Compared to chlorine, monochloramine produces fewer regulated disinfection byproducts, such as trihalomethanes, making it a safer option for long-term water treatment.
  3. Effective Against Biofilms: Monochloramine penetrates biofilms more effectively than chlorine, which helps control biofilm-associated pathogens like Legionella. This makes it particularly useful in reducing the prevalence of Legionella in plumbing systems, helping to prevent outbreaks of Legionnaires’ disease. (Related: Learn more about Legionella testing and water management plans.)

Limitations of Monochloramine

  1. Oxidizing Strength: Monochloramine is not as strong an oxidizer as chlorine, which can affect its ability to rapidly kill certain pathogens. This can be a limitation in situations requiring immediate disinfection.
  2. Potential Issues in Hospitals: The ammonia component of monochloramine can provide a nutrient source for non-tuberculous mycobacteria (NTM), posing potential health risks in hospital settings. Thus, its use in hospitals needs careful consideration and monitoring.
  3. Requires Chemicals: To produce monochloramines, sodium hypochlorite and ammonia are needed.

Comparison with Other Disinfectants



  • Powerful Oxidizer: Chlorine is effective at quickly killing a wide range of pathogens.
  • Immediate Disinfection: Chlorine provides immediate disinfection, making it suitable for rapid pathogen elimination.


  • Dissipation: Chlorine dissipates rapidly, necessitating frequent dosing, especially in hot water systems.
  • Ineffectiveness Against Biofilms: Chlorine is ineffective in penetrating biofilms and killing bacteria such as Legionella within the biofilms.
  • Rebound Growth Effect: Chlorine can cause a rebound growth effect when used for remediation where bacteria, after being stressed by chlorine, can regrow rapidly once chlorine levels drop.

Mixed Oxidant Solution (MOS)


  • Broad-Spectrum Killing: Provides broad-spectrum pathogen-killing abilities.
  • Effective at Penetrating Biofilm: Penetrates biofilm and kills pathogens.
  • No Chemicals Required: Inputs are only salt and water.
  • Maintenance: System is easy to maintain, clean and repair.


  • Frequent Dosing: Requires multiple dosing points due to quick consumption in water systems.
  • Water Quality: Water used to make the MOS must be treated with a water softener or reverse osmosis.

Chlorine Dioxide (ClO₂)


  • Strong Oxidizer: Chlorine dioxide has strong oxidizing properties and a broad range of disinfection capabilities.
  • Effective at Penetrating Biofilm: Penetrates biofilm and kills pathogens.


  • Rapid Consumption: Needs to be dosed frequently as it is used up rapidly.
  • Dosing Rate: Can only be dosed at 0.8 ppm often making it ineffective in hot water loops as the chemical dissipates too quickly and doesn’t maintain residual in the hot water loop.
  • Requires Hazardous Chemicals for Production: Either two or three precursor chemicals are needed, which may include acid, sodium chlorite and a reducing agent.
  • Maintenance:  Repairs are often expensive and complex.

Copper-Silver Ionization


  • Effective Against Specific Pathogens: Particularly effective in controlling Legionella and other pathogens in hot water systems.
  • No Chemicals Required: Input is a copper and silver bar that dissolves over time.


  • High Cost: Requires separate systems for each hot water loop, making it expensive and complex to implement for larger hot water systems.

Applications and Suitability

Monochloramine is suitable for large and complex plumbing systems due to its stability and prolonged disinfectant presence. Its effectiveness in reducing biofilm-associated pathogens like Legionella makes it an excellent choice for facilities such as prisons, office buildings, and other large structures. However, its use in hospitals should be carefully managed to mitigate the risk of NTM growth.

It is important to understand the specific needs and constraints of the water system under consideration, so contact an independent waterborne pathogen expert like Legionella Control Systems. Monochloramine can be effectively utilized to ensure long-term disinfection while addressing potential limitations in certain environments, and Legionella Control Systems can help you determine if your facility is a good candidate for the use of monochloramine.