Researchers set out to determine whether horizontal electric water heaters or geysers, which are common in most South African households, provide an environment that is conducive to the growth of Legionella, which thrive at temperatures ranging from 37ºC to 42°C.
Dr Wendy Stone from SU’s Water Institute conducted the interdisciplinary study with colleagues from the Institute for Biomedical Engineering and two departments in the Faculty of Engineering at 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 or geysers.
“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,” said Stone.
To determine the presence of Legionella, the researchers cut open water heaters shortly after they had failed mechanically and collected samples and biofilm (established communities of bacterial microorganisms) scrapings.
They also used microbiological techniques to assess the presence of Legionella at the point-of-use in the tap water from five active heaters, which they compared to cold water from the same source as a control.
Stone said the bacterial concentrations in the plumbing were as much of a concern as those in the heater tank.
“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,” she said.