Your health may be at risk from your daily shower

Bacteria that could cause severe pneumonia (legionnaires’ disease) may be lurking in your water heater or geyser, according to a study at Stellenbosch University (SU). 

“Our research highlights the connection between heating regimes (when and for how long a heater is switched on) and the increase in legionella, specifically the pathogenic species L. pneumophila, in water heaters (geysers),” says Dr Wendy Stone from SU’s Water Institute.

She conducted the interdisciplinary study with colleagues from the Institute for Biomedical Engineering and two departments in the Faculty of Engineering at SU.

In the study, which was published recently in the academic journal Energy for Sustainable Development, the researchers set out to determine whether horizontal electric water heaters or geysers (common in SA households) provide an environment that is conducive to the growth of legionella, which thrives at temperatures from 37 to 42°C.

Stone says that in South Africa there is no information about the prevalence of legionella in domestic water heaters, which normally heat water to 65°C. However, since temperatures as low as 40°C are considered sufficient for user satisfaction, many users who struggle financially choose to operate at a lower temperature or turn off their water heaters to save money.

To determine the presence of legionella, the researchers cut open water heaters shortly after they had failed mechanically and collected samples.

According to Stone, the bacterial concentrations in the plumbing between the water heater and the taps were as much of a concern as those in the heater tank. “Our results show that the lower surfaces of the heater remaining at temperatures below 45°C create an ideal environment for legionella growth,” says Stone. “The cold tap showed no legionella, suggesting that the heater provides the temperatures necessary to stimulate growth, either within the heater or in the distribution system directly downstream of the heater.

“The heater and its hot water distribution system could be creating ideal temperatures for the growth of legionella.”

Stone points out that for healthy individuals, the risk of legionella infection by the low bacterial concentrations found in taps is slim to none.

However, the WHO identifies pulmonary illness and weak immune systems as important risk factors in contracting legionellosis, she adds.

Stone says because the symptoms of legionellosis can often be confused with more common forms of pneumonia, the extent of the disease may be significantly under-reported in South Africa since few people are aware of it, and it’s likely hidden by TB and all the other medical crises associated with compromised immunity. The exact impact, especially on individuals with weak immune systems, is simply unknown.

“Given that legionella was detected in the water heaters, we plan to do more work to establish the health impact.”

According to Stone, the mode of infection is via water droplet inhalation, for example when taking a shower or a bath or washing the face at the sink, and not through ingestion. As a result, “this research informs us that we can mitigate the risk by regulating our water heaters better, and indicates no risk of contracting legionellosis from drinking tap water.”