In contemplating different water treatment options hospital engineers, infectious disease specialists and even the board and executive often have very differing opinions on what is the best method. What they all want to achieve is an efficient and safe system that delivers Legionella control.

There are a range of operational controls, which should be implemented to reduce risk.1. However the cornerstone of an effective program in healthcare settings is the choice of systemic water treatment to prevent microbial and legionella proliferation.

To achieve effective disinfection in hospital drinking water systems a systemic treatment is required, that is a treatment that disinfects all water circulating throughout the distribution system.

Disinfecting the drinking water system is an effective preventative measure.2.

Ideally a systemic disinfection program will:

  • effectively remove pathogens over a range of physical and chemical conditions
  • produce a disinfectant residual that is stable and easily measured
  • produce no unacceptable by-products
  • cause minimal damage to assets (plumbing & associated components)
  • be easily generated and safe to handle
  • cost-effective3

An effective systemic disinfectant treatment must create sufficient residual effect downstream to decontaminate the water throughout the facility.

Options for Systemic disinfection of water to prevent Legionella.

There are a few rules of thumb that should be followed:

Ultraviolet (UV) light:  Many health facilities, in an effort to minimise harm, employ UV radiation as their systemic water treatment. Unfortunately UV radiation generally fails in this application as it has no disinfectant effect once the water passes the UV lamp.  Microorganisms in fact can repair their damaged DNA through photoreactivation and base excision repair.

Particulates can also shade the bacteria from the light reducing the effectiveness of the UV.  Legionella often lives in a host amoeba and therefore the Legionella is protected from the UV.1.

We have also found UV systems are not sized correctly for the water flows nor maintained sufficiently to provide effective exposure.  This is why UV is generally best reserved as an additional barrier at the point of use for water used in high risk clinical settings such as a transplant or an oncology ward.

An Oxidising Disinfectant, such as chlorine, chlorine dioxide or mono-chloramine all have the capacity to provide an effective disinfect residual throughout a health facilities’ reticulated water system.  The selection of an oxidising disinfectant has to be made after careful analysis of the incoming water quality, the layout and physical and chemical condition of the entire water distribution system.

A system that is relatively uncomplicated with few Legionella detections can be effectively managed with a well monitored program that achieves a chlorine residual of up to 0.05 ppm. However in larger systems with issues of stagnant water or low flow, established biofilm and a high frequency of positive Legionella  the use of a an oxidising biocide such as chlorine dioxide or mono-chloramine may well be the preferred option to achieve effective control.

Health facilities must manage their microbial risk; however the long-term impact of the disinfectant on the water system assets should also be taken into account. The high oxidising capacity and ability to penetrate biofilm of chlorine dioxide and monochloramine means less is required to achieve effective disinfection. Consequently these oxidising disinfectants can be a better choice in achieving microbial control and minimising the corrosive effect of the treatment.

Suitable Systemic Water Disinfection Methods

Preventative DisinfectionLegionella detections up to % of outlets Effectiveness in Cold WaterEffectiveness in Not Water systemsEffecteved by Water hardness and pHControls Biofilm HCC. 500 cfu/mL
Chlorine Dioxidexxxx
Cu/Au ionisationxxx

Minimisation of byproducts that cause health concernsAsset ManagementEase of monitoringUse in remedial actionCost effectiveness
Chlorine Dioxidexxxx
Cu/Au ionisationx

Monochloramine has been used in hospitals internationally because of its very persistent residual, which appears has provided better control in extensive plumbing systems. The stability of monochlormaine has also resulted in higher disinfectant concentrations in hot water. In a 2 year prospective, environmental study the legionella colonisation was reduced from 60% of hot water systems under a chlorine regimen to only 4% of hot water systems after conversion to monochloramine.5

Legionella Colonisation

Effectiveness for Systemic DisinfectionSystem best suited
ChlorinexSmall to medium sized
Few Legionella detections
Chlorine dioxidexMedium to large systems
Established Biofilm
Multiple deadlegs
MonochloraminexLarge systems, with extensive pipework
Established biofilm
Hot water systems
Cu Ag IonisationxSmall to medium sized
UV light*Not effectivePOU high risk clinical settings
Not effectivePOU high risk clinical settings

Copper-silver ionisation of water systems has the advantage of not corroding piping or plumbing fixtures and is effective at all water temperatures. However the effectiveness of ionisation is reduced by water hardness and the pH of the water. Copper precipitation has been found It can be difficult for correct dosing to be achieved. Resistance of Legionella to Copper-silver ionisation has also been reported in hospitals overseas.2.

Ozone is a highly effective disinfectant but has no residual to measure efficacy, hence is not suitable for systemic use.  Ozone also of limited application even at point of use as it is highly reactive, corrosive, expensive and a potentially toxic.

The most effective programs are often a combination of a systemic disinfection of the entire water system and local disinfection in sections where people are at greatest risk. 

The New Australian Guidelines for Legionella Control in health facilities

The new Australian Guidelines for Legionella control in the operation and maintenance of drinking water distribution systems in health and aged care facilities.

The new Australian guidelines recommend a multi-barrier approach to control Legionella in healthcare settings. Temperature control is limited within a health care facility due to the need to deliver water at temperatures <50°C to avoid scalding. Flushing programs are intrinsic to an effective program to prevent stagnation in unused rooms. However these two steps alone are often insufficient to provide control of Legionella and other water borne pathogens in the potable water supply.

As the systems and sites vary, so do our recommendations as to the best method to control Legionella.  HydroChem recommends a comprehensive range of measures to reduce the risk for the individual site, including flushing, temperature control, cleaning of outlets and a meticulously monitored water treatment program.

  1. Guidelines for Legionella control in the operation and maintenance of drinking water distribution systems in health and aged care facilities. enHealth Oct 2015
  2. Lin, YE, Stout JE, Yu VL 2011 Infect Control Hosp Epidemiol 32(2):166-173
  3. Australian Drinking Water Guidelines
  4. Lin YE, Vidic RD, Stout JE, Yu VL 2002 Applied and environmental microbiology p 2711-2715
  5. Flannery B et al. 2006 Emerging Infectious Diseases. Vol 12, No. 4 pp 555 – 596