The water-borne pathogen best known for Legionnaires' disease, although it also causes Pontiac fever and Lochgoilhead fever. It's contracted by inhaling small drops of water, (aerosols), not by drinking.


It multiplies between 20 and 45°C. The current recommended temperature for hot water systems is 55°C, but there's increasing scientific evidence that Legionella can survive above this level. Lower temperatures make it less active. Long-standing water gives it more time to multiply. Deposits such as rust, scale and biofilm can protect Legionella (and other bacteria) from a range of measures introduced to control them. Reference

Health and Safety Executive, (2014) HSG274 Part 2: The control of Legionella bacteria in hot and cold water systems, para. 2, p.3 “There is a reasonably foreseeable Legionella risk in your water system if:

  • water is stored or recirculated as part of your system
  • the water temperature in all or some part of the system may be between 
20–45 °C;
  • there are deposits that can support bacterial growth, such as rust, sludge, scale and organic matter;
  • it is possible for water droplets to be produced and, if so, if they can be dispersed;
  • it is likely that any of your employees, contractors, visitors etc. could be exposed to any contaminated water droplets.”


Not everyone will catch Legionnaires' disease - groups especially at risk include the elderly, newborn, heavy smokers and drinkers, people suffering from lung, heart or kidney disease, diabetics and those who are immune-compromised, e.g. transplant patients. Reference
“Everyone is potentially at risk of developing Legionnaires’ disease. (NHS) However, certain things make it more likely that you will experience a more severe form of the infection. These include:
  • being 50 years of age or over – 235 (83%) of the 284 confirmed cases in 2013 involved people over 50 years of age
  • smoking, or having smoked heavily in the past (a recent study has shown that smoking cannabis may also increase your risk)
  • drinking alcohol heavily
  • about three-quarters have an underlying medical condition, such as diabetes, kidney disease, or a pre-existing lung condition
  • having a weakened immune system – for example, people with HIV and AIDS or cancer.”

% samples positive for Legionella at 7 UK hospitals using the Orca system

Hospital 1

A 650-bed hospital in the south-east of England

% samples positive for Legionella

Hospital 2

A 700-bed hospital in the Midlands

% samples positive for Legionella

Hospital 3

A 430-bed hospital in the Midlands

% samples positive for Legionella

Hospital 4

A 600-bed hospital in the South-East

% samples positive for Legionella

Hospital 5

A new wing of a large London hospital

% samples positive for Legionella

Hospital 6

A 900-bed hospital in the South West

% samples positive for Legionella

Scientific Evidence

  • Infection Control Hospital Epidemiology

    Lin, Y.E., Stout, J.E., & Yu, V.L., (2011), Controlling Legionella in Hospital Drinking Water: An Evidence-Based Review of Disinfection Methods, Infect Control Hosp Epidemiol 32(2):166-173.

    The authors conduct a literature review of papers covering copper-silver ionisation, chlorine dioxide, monochloramine, UV light, hyperchlorination, point-of-use filtration and superheat-and-flush. In it they state that CSI is the only control method for which multiple evaluations of its effectiveness have been published in peer-reviewed scientific papers, and conclude that it appears to be the best technology available for controlling Legionella in hospital water systems.

  • Clinical Infectious Diseases

    Liu Z., Stout, J.E., Boldin, M., Rugh, J., Diven, W.F., and Yu, V.L., (1998), Intermittent use of copper-silver ionization for Legionella control in water distribution systems: a potential option in buildings housing individuals at low risk of infection. Clin Infect Dis 26: 138–140.

    Of three buildings colonised with Legionella, two were fitted with copper-silver ionisation systems, with the third building left as a control. Positive tests for Legionella in the first building dropped to zero within four weeks, and to zero within the second building within twelve weeks. Recolonisation didn’t occur in the first test building for 6-12 weeks after the CSI system had been switched off, and in the second building for 8-12 weeks. The control building remained positive throughout.

  • Infection Control Hospital Epidemiology

    Stout, J.E. & Yu, V.L., (2003), Experiences of the first 16 hospitals using copper-silver ionisation for Legionella control: implications for the evaluation of other disinfection modalities, Infect Control Hosp Epidemiol 24(8): 563-8.

    The first 16 hospitals in the USA to install copper-silver ionisation were surveyed twice, in 1995 with a follow-up in 2000. All had reported cases of hospital-acquired legionnaires’ disease prior to installation, and 75% had attempted other control methods. In 1995 50% of the hospitals reported 0% positivity, and 43% still reported 0% in 2000. Moreover, no cases of hospital-acquired legionnaires’ disease had occurred in any hospital since 1995.

  • American Journal of Infection Control

    Miuetzner, S. et al, (1997), Efficacy of thermal treatment and copper-silver ionization for controlling Legionella pneumophila in high-volume hot water plumbing systems in hospitals, American Journal of Infection Control, Vol. 25, No. 6, p. 452-457.

    Hot water (>60 oC) was flushed through fixtures for 10 minutes. Copper-silver ionisation units were installed upstream from hot water tanks. It was found that four heat-flush treatments failed to provide long-term control of Legionella, whereas ionisation reduced the recovery rate of Legionella from 108 outlets from 72% to 2% within 1 month and maintained effective control for at least 22 months.

  • Clinical Infectious Diseases

    Mòdol, J. et al, (2007), Hospital-Acquired Legionnaires Disease in a University Hospital: Impact of the Copper-Silver Ionization System, Clinical Infectious Diseases, Vol. 44, No. 2, p. 263-265

    Hospital-acquired legionnaires’ disease had been endemic in a Barcelona hospital for many years, with various control methods tried and failed. After installation of a copper-silver ionisation system, Legionella colonisation decreased significantly and the incidence of hospital-acquired legionnaires’ disease decreased dramatically from 2.45 to 0.18 cases per 1000 patient discharges.

  • The Journal of Infectious Diseases

    Liu, Z. et al (1994), Controlled Evaluation of Copper-Silver Ionization in Eradicating Legionella pneumophila from a Hospital Water Distribution System, The Journal of Infectious Diseases, Vol. 169, No. 4, pp. 919-922

    A copper-silver ionisation system was effective in eradicating Legionella from the hot water distribution system of a hospital building were identified as easy installation and maintenance, non-toxic by products well below EPA standards, stable and easily measured residual that was unaffected by high temperatures, and a margin of safety if the system stopped working as recolonisation by Legionella required more than 2 months.

ProEconomy's reputation speaks volumes and the Orca system is highly regarded by those who have installed it.