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Temperature control in water systems

From our partner Rotronic we highlight equipment for effective temperature control in water and ventilation systems to avoid bacteria

In 1976, 182 attendees at a convention hosted by the American Legion Veterans Association of Philadelphia at the Bellevue-Stratford Hotel in Philadelphia contracted a serious case of pneumonia, 29 of whom died.

The public health authorities then launched an intensive investigation into the then unknown causes of the mass disease, which became known as Legionnaires’ disease. Unwittingly mass-produced by the hotel ventilation system. “Legionnaires’ disease” (Legionellosis), which is triggered by inhalation, shows symptoms of febrile pneumonia, which causes death in about a fifth of cases if not treated properly.

As the main route of infection was identified as inhalation of respirable aerosols, all equipment and systems that blow, spray, drip or atomise water were called into question. This includes showers, aerators at the outlets of water systems and other sources.

What are legionellae?

Legionellae are rod-shaped, motile bacteria 2-5 µm long and 0.5-0.8 µm in diameter. They occur in many species and groups around the world, usually in surface waters and soils.

Legionella, legionellosis, temperature control in water systems and refrigerators and ventilation systems
Image: legionella
Disease risk of legionellosis

Legionella pneumophila is responsible for more than 90% of serious cases of Legionellosis. The incubation period is between 2 and 10 days. People with weakened immune systems (elderly, smokers, diabetics, etc.) are most at risk. Legionellosis is not contagious.

The risk of infection depends on the concentration of Legionella, the pathogenicity of the strains and the resistance of the people affected. Legionella in the water systems of hospitals, retirement homes, rehabilitation centres and other care facilities can therefore have particularly serious consequences. To avoid risks, contamination limits (CFU) should be as low as possible (below 1000 CFU/l). Higher risk areas such as transplant centres, laboratories, intensive care units, etc. should be completely free of Legionella (0 CFU/l).

Reducing the risk of legionella in drinking water installations – temperature control in water systems

As legionellae find optimal conditions for reproduction in stagnant water, in the temperature range between 25 and 55 °C, these conditions should be avoided by the use of hydraulically balanced circulation lines to the points of discharge and a discharge water temperature of at least 60 °C. This problem is solved by having the right water temperature in all circulation lines. If there is a maximum of 3 litres of tap water down the drain, the hot water temperature is above 55 °C and the cold water temperature is below 25 °C, these are the optimal conditions for Legionella to occur in a drinking water distribution system.

It should be borne in mind that unsuitable materials for water pipes (galvanised pipes, uncertified plastic pipes, etc.) lead to the formation of biofilms (deposits of micro-organisms). They are a breeding ground for Legionella, which multiplies on the inside of the pipe.

One of the preventive measures to avoid Legionella is “thermal disinfection”. This shall be achieved by heating (by draining water above 70 °C) water heaters, water tanks and the entire hot water pipe system, including taps, for a minimum of 3 minutes.

This is not possible in the case of dead pipes, sprinkler pipes and hydrant pipes. The entire drinking water distribution system should be free of stagnant water (i.e. water that has not moved for more than 4 hours), as this can lead to water temperatures between 25 and 55 °C and associated Legionella.


The advantage of proper thermal disinfection is that Legionella can be safely and reliably killed even in biofilms without the use of chemical additives. The downside is that there is no guarantee that the biofilm will be permanently removed. In addition, the process puts strain on the pipe material, increases the risk of corrosion and can cause burns at the points of dispensing.


In this process, the tap water is surrounded by waves of high-energy UV radiation (wavelength 254 nm). This attacks the genetic make-up of Legionella, preventing it from reproducing. Filters at water points can trap Legionella, but this method does not remove them from the drinking water system and does not reduce biofilms.

ELPRO Lepenik & Co. offers you a complete solution for temperature control in water systems, refrigerators, ventilators and more from our Rotronic product range. In addition, you might also be interested in the ELPRO temperature sensor programme and EBRO temperature gauges.


Gateway RMS-GW-868

For successful temperature monitoring in water systems and elsewhere, the Gateway interface is indispensable for connectivity between the wireless data logger and the server software. It can manage up to 60 data loggers at the same time, collecting all the measurement data from the wireless logger and transmitting it to the server software. When multiple inputs are used in the same network, they are configured individually. If one input fails, the measurement values are automatically sent to the server software via another input.

Temperature mini data logger RMS-MLOG-T10-868

The wireless mini data logger in the Rotronic control system is truly flexible and cost-effective thanks to its small housing and wireless interface. Its versatility allows it to monitor refrigerators, incubators and water pipes.

Sensor T10-0004

T10-0004 was developed specifically for measuring the temperature of pipes to check for legionella or to monitor the temperature in a pipe system. T10-0004 can be installed using a hose clamp.

RMS software

For a comprehensive temperature control of water systems, we also stress the importance of the RMS software, which makes all measured values available in a structured format from a central point. The RMS reporting function allows you to receive all the selected statistics at a specified interval via webmail.

Author Katarina Žunko
May 2021

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