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DVGW research project: growth of legionellae in cold water starts at 30°C, operational temperatures up to 25°C are uncritical

The DVGW Center of Technology Water (TZW) has examined the growth of legionella bacteria in potable water cold. The findings are interesting and should calm all plant operators and owners who are not capable of keeping cold water temperatures under 25°C. According to the TZW significant multiplication of legionellae begins at 30°C.

Quelle: Energie Wasser-Praxis Mai 2020

The applying european and german codes of practice for drinking water stipulate that installations for potable water cold have to be operated in a temperature regime that shall not exceed 25°C 30 seconds after opening the sampling valve to guarantee hygienically safe operation of the system. 

For quite some time, there has been a controversy among experts if legionella growth is really impossible at permanent temperatures of 25°C. The TZW-research project that legionella do not grow in such temperatures and that therefore a potable water system run under the regime of the european and german technical rules is safe and poses no harm for the health of inhabitants and users.


Growth of legionellaes starts at 25°C and increases with rising temperatures. A little increase of bacteria colonies was detected at 27°C, a significant rise at 30°C. Short-term rises in temperatures above 25°C show no effect.

Material and dimensions of water pipes

In all tests in the lab model legionella in the biofilms of the rubber hose grow significantly faster than in the copper or steel pipes. Dimensions of the pipes influence the biolfilm building since with decreasing diameter the ratio of surface to volume increases showing more effects of surface processes of the water body.

If legionella are detected at water samplings with temperatures under 25°C the TZW-scientist assume that the occurance is caused by temporarily increased operational temperatures or thermal bridges.

A recap of the research results is available in the internet under:

Evaluation of 105,000 drinking water data sets show 200 legionella test results under 25°C

The assessment of our own 105,000 drinking water data sets (a part of it was provided for the UBA-study "legionella in drinking water" 2016) questions the conclusion of the TZW-researchers that the mere cause is the temporary rise of the operational temperatures. We see 405 positive legionella results at temperatures of 30°C of 4.398 test results total with cfu-values > 100. Still 199 result show a at least a medium contamination > 100 cfu at temperatures<=25°C  at the time of sampling from the valve. After a constant temperatures was reached still 72 show legionella at (<30°C) to 55 (>25°C). Further research work needs to be done to see clearer.

Drinking water check-ups for legionella offered to enterprises re-opening their offices

Due to covid 19 many industrial, commercial and public buildings have not been used for several months. Since the numbers of new infections with the corona virus have been going down lately companies take a shot at re-opening their businesses. If in the facilities re-opening now drinking water installations have not been in operation or have not been flushed in certain intervals water stagnation may have led to exponential growth of biofilms and - along with that - pathogenic bacteria such as pseudomonas aeruginosa and legionella in the pipes. 

We offer all firms (before re-opening) a thorough check-up of the drinking water for legionella and other pathogenic germs to attractive conditions. Do not hesitate to ask us. We work for German industries as well as for Anglo-American companies from commercial and industrial branches that run subsidiaries in Germany.



Although coming from the housing sector we have seen an increase in business relations with industrial  enterprises. Before the German drinking water directive passed the Bundesrat firms of the producing and processing industry have always been very sensitive for safety issues. Labor protection laws ordered them to have the water used or processed tested for potentially pathogenic bacteria.

Gas leak detection with GAS-Control

WATERcontrol has evolved from the "big sister" GAS-Control GmbH, a specialist for preventive gas safety checks within builidngs. GAS-Control has worked for the German housing industry for 25 years.

To detect gas leakages, even on concealed lines, the firm operates with portable gas leak detectors that pinpoint tracers of natural gas where they escape from the pipe.