Measuring instruments for the prevention of legionella

Legionella are bacteria that occur naturally in our waters. From there, they can colonize supply systems and enter sanitary water systems or technical equipment via the water distribution network. Legionella bacteria find ideal growth conditions at temperatures between 25 and 45 °C. Health-threatening concentrations occur in the range of 20 to 55 °C.

It is therefore problematic if systems for water heating are operated at temperatures that are too low. Longer standing time of water in pipes also promotes bacterial reproduction. In addition, conserving energy and water for environmental or cost reasons can encourage the spread of legionella.

There are various technical options to reduce the number of pathogens or to sanitize the entire system in case of a massive infestation. However, it makes more sense to prevent colonization from the outset. One of the most effective prevention measures in this regard is to monitor or measure water temperatures at various locations.

Testo offers you various measuring instruments for this purpose - from simple thermometers to digital temperature measuring instruments and data loggers. This allows you to precisely and reliably check the water temperature in hot and cold water systems.

Good to know:

  • The temperature in final storage tanks for water must not be below 60 °C.
  • If hot water comes from a central storage tank via circulation, the temperature must not be below 55 °C even in the return flow.
  • In cold water systems, the water temperature must be kept at < 20 °C.
  • In systems for heating drinking water, the heating system must be able to raise the water temperature to 70 °C or more to ensure disinfection.

Measurement of water temperature


Digital temperature measuring instrument testo 925

With the testo 925 thermometer and its broad range of temperature probes, a wide variety of measurements can be carried out in heating, sanitary, refrigeration and air-conditioning technology.

  • Easy, fast and precise measurement with thermocouple Type K probe
  • Audible alarm sounds if a limit value is exceeded

Suitable probes


Temperature kit testo 915i

Wireless measurements in various applications are possible with the testo 915i kit and its exchangeable temperature probes.

  • Easy operation, evaluation and documentation with cost-free testo Smart App

  • Exchangeable temperature probe TC Type K, Class 1:

    • Air probe
    • Immersion/penetration probe
    • Surface probe

Waterproof mini thermometer

With the mini thermometer, the outflow temperature can be measured easily and quickly at all points of the system.

  • Display of max./min. values
  • Waterproof – protection class IP67
  • Measurement range: -20 to +230 °C

Continuous monitoring of the water temperature


Temperature data logger testo 175-T2

The testo 175-T2 data logger makes it easy to continuously monitor the water temperature at the pipes.

  • Recording of 2 temperature values / internal & external (NTC)
  • Display of min-/max.


Temperature data logger testo 175-T3

The data logger testo 175-T3 has two TC connections - ideal for simultaneous measurement of hot and cold water pipes.

  • For measuring low and high temperatures.
  • Data analysis through software


Radio data logger testo Saveris 2-T3

The testo Saveris 2-T3 wireless data logger has two TC connections for simultaneous measurement of two temperature values.

  • Automatic measured value documentation / data transmission via WLAN
  • Alarms when limit values are violated
The specially designed pipe wrap probe for the data loggers provides building owners, facility managers and contractors with an optimized solution for monitoring the temperature of cold and hot water pipes.

Thanks to its spring mechanism, this can be attached to the pipe quickly and with just one movement. The variable spring tension means the pipe diameter is irrelevant, the probe is always securely attached, which is indispensable for an accurate measurement. In addition, the probe adapts to the pipe temperature within a very short time and also registers temperature changes correspondingly quickly.

Determination of the pH value for the analysis of drinking water

The pH value is an important parameter when testing for legionella and determining water quality. The water samples taken must be checked for their pH value directly or immediately after sampling, as it would change of the course of storage.

When chlorine is used to disinfect the water, the pH value is relevant. The disinfecting effect of chlorine decreases at a pH value above 7, so that the chlorine concentration must be adjusted accordingly.

pH-/temperature measuring instrument testo 206 pH 1

  • TopSafe: Dirt-proof protective cover
  • Maintenance-free gel electrolyte
  • Protection class IP68
  • Measurement range
    0 bis 14 pH
    0 to +60 °C
  • Battery time: 80 h (Auto Off 10 min)


Legionellosis, or Legionnaire's disease, is an infectious disease caused by bacteria of the genus legionella. If legionella bacteria encounter suitable living conditions, they can multiply rapidly at high concentrations.

Transmittal to humans is in principle possible through contact with tap water. If bacteria are ingested through eating or drinking, they are as a rule harmless. Only when aerosol is formed and the bacteria-containing water is inhaled can it lead to a risk of infection or illness in humans. Every responsible homeowner or system operator should therefore ask themselves whether legionella can multiply in their installations.

Especially for those responsible for old people's homes, hospitals, care facilities, schools, swimming pools, hotels and other public facilities with showers, there is a legal obligation in many countries to ensure perfect water quality. But operators of cooling towers, air conditioning systems and humidification systems must also be able to assess the legionella risk for their system.

Legionella detected – what’s to do?

If by using temperature data loggers you have established that the temperature values of a water supply system have been moving in the critical range between 20 and 50°C over a longer period, the various methods for combating legionella are available to you.

  • Thermal disinfection involves hot water at 70°C being run for three minutes through all drawing points, because the bacteria die off at this temperature. Depending on the size of the plant, thermal disinfection can also be carried out in sections.
  • Chemical disinfection involves the use of chlorine products which kill off the legionella pathogens. Ozone or chlorine dioxide can also be used, because these do not produce any undesirable by-products.
  • If you want to avoid the use of chemicals, the impulse rinsing process is a good option. Sediments and biofilms, which constitute a nutritional base for bacteria, are removed using compressed air bubbles introduced into the water transport systems.
  • It is possible to impair the genetic information of microorganisms by ultraviolet irradiation of drinking water, which means their reproduction through cell division is inhibited.



Further information about facility management

Brochure – Measurement technology for prevention of legionella

Measurement technology and services for technical facility management

Measurment of indoor air quality and thermal comfort in the workplace