Monochloramine and building water systems: cause for concern?

Monochloramine in some jurisdictions is replacing chlorination as the water utility disinfectant. Monochloramine gives better biofilm penetration and longer residual times in the distribution and pipelines than chlorine. This makes monochloramine a better option for long pipelines where maintaining residuals can be a problem. This all sounds good but problems arise once it passes through the meter and enters your building water system.

What is monochloramine?

As the diagram below shows monochloramine is made by mixing a 1:1 ratio of chlorine and ammonia. To ensure all the chlorine is converted to monochloramine a small excess of ammonia is added. The monochloramine is then distributed to the end user, occasionally a top-up dose is delivered on long pipelines. Monochloramine persists best in mildly alkaline water below 30 Celsius. In the water distribution system environmental conditions are comparatively stable making the disinfection process relatively effective and predictable. The problems arise once the water leaves this stable environment.

Water distribution vs building water systems

The ownership, and so responsibility, for the water quality ends at the meter - and so does the microbial ecology! After the relatively stable environment of the distribution network the water enters the chaotic environment of a building water system. Almost every environmental condition changes. Almost every change is favourable for microbial growth. The table below describes these.

Mains Water Pipelines	Buildings Hydraulic System
Consistent water flow	Intermittent water flow
Relatively low Surface Area : Vol ratio	High Surface Area : Vol ratio
Consistency of construction materials	Extremely variable construction materials
Lower water temperatures	Higher water temperatures
Reasonably consistent disinfectant residual	Variable low disinfectant residual
Short residence times	Long residence times

So the microorganisms that survive disinfection (and we know they do!) enter a new environment that provides a range of temperatures, materials, surface areas, flow and stagnation, and reduced disinfection. It's pretty much a microbial adventure park!

Those microorganisms that escape the mains supply disinfection enter the building water system and begin colonisation. Any disinfection residual that comes in with the mains supply will soon be lost so why is monochloramine any different?

Monochloramine and Microorganisms

Monochloramine has been shown to have a similar efficacy to chlorine in distribution systems. Studies have shown that both Legionella and non-tuberculous Mycobacteria survive and multiply in both chlorinated and monochloraminated distributions (Whiley et al, 2014).

Studies have also shown the long term survival of Legionella in monochloraminated water (Alleron et al 2008) and induction of the Viable Non-Culturable state (VBNC, Alleron et al 2006, Casini et al 2018). Simply put this means that Legionella survive and become undetectable in monochloraminated water given the right growth conditions.

The story is similar for Mycobacteria and other potable water microorganisms. In fact protozoa that Legionella parasitise may be less susceptible to monochloramine than chlorine too (Wang et al 2012).

But there is more to the story......

Nitrification

Nitrification is a biological process that captures ammonia and converts it to nitrate. Nitrate is a much more readily available nutrient to microorganisms. The process of nitrification occurs in biofilms containing nitrifying bacteria. Studies have shown the majority of chloraminated water supplies contain nitrifying bacteria (Cunliffe 1991, Bradley et al 2020).

Remember the small excess of ammonia included in the chloramine production process? Once inside the biofilm rich environments of your building this ammonia becomes the feedstock for nitrifying bacterial biofilms. The biofilms will establish quite rapidly depending on how much ammonia is available. Once established they will be providing a continuous supply of nitrate to other microorganisms. All this nutrient is then distributed around the building via a recirculating loop.

It would be bad enough if it stopped there - but nitrifying biofilms will actively break down monochloramine to release the ammonia. An active nitrifying biofilm significantly increases chloramine decay rates. This means the biofilm is actively feeding on the disinfectant and providing nutrients to the rest of the microbial community including Legionella (that now evades culture). In some instances nitrification can reduce the persistence of chloramines in a building water system below that of chlorine. A spin-off of this activity is changes in pH and increased total chlorine contributing to elevated corrosion rates.

This is not hearsay, and a full and detailed review of this phenomenon was published in 2020 (Bradley et al 2020). This process is facilitated by the environment within the building water system as it processes the 'feedstock' of chloraminated water from the distribution. If you want to check your building now do a quick ammonia test - your local aquarium shop will have a test kit. A result above 0.3 - 0.5 mg/L Ammonia came from your building not from the water utility. Our experience is Ammonia concentrations can exceed 3 mg/L in large buildings due to nitrification. These sort of values can become an issue for RO systems and dialysis.

Obviously once this situation has occurred there is a challenge for disinfection. Not only the biofilm deposits around the system but also the existing disinfectant residual (monochloramine) need to be considered.

Free chlorine conversion (FCC) is a strategy used in United States chloraminated drinking water systems to control nitrification. This process involves temporarily replacing monochloramine with free chlorine as the disinfectant. This process can effectively reduce total bacterial load in a water distribution system. Beware through, bacterial load is reduced during the chlorination phase, but returns to previous levels once chloramination is restored.

Disinfection issues

First and foremost remember your Hierarchy of Control - things need to be put in place that will give you the best chance of a successful disinfection. A Water Safety Risk Management Plan is essential. Many jurisdictions will specify either chlorination or pasteurisation for disinfection. As we have discussed in previous Blogs pasteurisation is not an option for contaminated cold water systems that aren't very cold!

The next problem is that chlorine reacts with monochloramine. Many will be familiar with the term 'breakpoint chlorination'. This is often applied to swimming pools where ammonia from bathers is converted to chloramines creating that 'pool chlorine smell'. Chlorine is added until all the monochloramine has been oxidised. Once this 'breakpoint' is achieved then chlorine can be added to get a disinfectant residual.

Of course this reaction takes time and contact both of which are obstacles in a building water system. In practice true breakpoint chlorination cannot be achieved in an active water system like it can in a swimming pool. There is also the chance that unwanted disinfection byproducts (DBPs, dichloramines and trichloramines) can be created. However with good process control a 'de facto' breakpoint chlorination can be achieved. This involves a little technical know-how and good control but can successfully chlorine disinfect the system.

A better alternative is activated carbon filtration of the supply from the meter followed by chlorination. This costs more but has better control and avoids issues with DBPs.

Summary

Sorry, there isn't very much good news in this story. If your water utility uses monochloramine to disinfect your supply then you are at risk of nitrification. If nitrification is happening then you can safely assume there is a well established biofilm community in your system. This in turn means more accommodation for Legionella and protozoa in a disinfectant compromised environment.

It is worth knowing how the water entering your building is treated. If your supply is monochloraminated then more intensive monitoring of chlorine residuals and more frequent disinfection need to be considered. Routine testing for ammonia may also need to be added to the list.

As and aside - a carbon filter on your fish tank may save you some unwanted casualties as well! They don't like either the ammonia or the nitrite.

All of the mentioned areas above are what we specialize in, our business delivers industry leading processes, systems, training and support as well as market leading disinfection products that will enable you to manage and reduce risk of waterborne infection. We are an ISO accredited business and hold Systems, Safety and Environmental certification, please feel free to contact us if you would like to talk more.

References

Alleron, L., Merlet, N., Lacombe, C., Frere, J. 2008. Long-term survival of Legionella pneumophila in the viable but nonculturable state after monochloramine treatment. Curr. Microbiol. 57: 497-502

Alleron, L., Frere, J., Merlet, N., Legube, B. 2006. Monochloramine treatment induces a viable-non-culturable state into biofilm and planktonic Legionella pneumophila populations. In: Legionella: State of the Art 30 years after its Recognition. ASM Press

Bradley, T., Hass, C., Sales, C. 2020. Nitrification in Premise Plumbing: A Review. Water 12:830

Buse, H.Y., Mistry, J.H. 2024. Microbial and physicochemical water quality changes within distribution and premise plumbing systems during a chlorine conversion. PLOS Water, Feb 8, 2024

Casini, B., Buzzigoli, A., Cristina, M., Spagnolo, A. et al. 2014. Long-term effects of hospital water network disinfection on Legionella and other waterborne bacteria in an Italian university hospital. Infect. Control Hosp. Epidemiol. 35(3): 293-9

Cunliffe, D.A. 1991 Bacterial nitrification in chloraminated water supplies. Appl. Environ. Microbiol. 57(11)3399-402

Wang, H., Masters, S., Hong, Y., Stallings, J. et al 2012. Effect of disinfectant, water age, and pipe material on occurrence ans persistence of Legionella, mycobacteria, Pseudomonas aeruginosa, and two amebas. Environ. Sci. Technol. 46: 11566-11574

Whiley, H., Keagan, A., Fallowfield, H., Bentham, R. 2014. Detection of Legionella, L.pneumophila and Mycobacterium Avium Complex (MAC) along potable water distribution pipelines. Int. J. Environ. Res. Public Health 11(7):7393-7405