Turning down the temperature on your home geyser is a fast way to save on electricity, money, and your share of greenhouse gas emissions, and turning your geyser off when not needed is even better.
But it could also put you at risk of the pneumonia-like Legionnaires' disease that has a high fatality rate when coupled with some of South Africa's most prevalent diseases, TB and HIV – and can even strike down a cabinet minister with access to high-level treatment.
Working with a plumbing company, researchers at the University of Stellenbosch cut open burst geysers and studied their bacterial content. They also tested water coming out of taps, and used fluid dynamics modelling to look at the temperature distribution in horizontal geysers.
Due to the temperature variation in geysers themselves, Legionella is unlikely to survive there, the researchers say in their paper published in the journal Energy for Sustainable Development. But it does seem to survive in the downstream piping running to taps, unless it is regularly subjected to scalding temperatures.
"The simplest fix for certain is setting geysers at higher temperatures," lead author Dr Wendy Stone told Business Insider South Africa.
Without such sterilisation of pipes, Legionella can be carried into bathroom steam and inhaled.
The good news: heathy people are unlikely to develop Legionnaires' disease from such exposure, the researchers say. The bad news: add in the HIV and TB prevalent in South Africa, and the odds of getting ill – and dying – increase dramatically.
"We have emphasised that people with high immunity don't have to worried," said Stone. "But they are also more likely to limit their risk with higher temperatures."
On the other side of the coin, lowering temperatures or shutting off geysers during certain parts of the day, seem to increase the risk.
Legionnaires' is often contracted via air-conditioning systems that make inhalation easy, but the actual prevalence in South Africa is not know. It presents as pneumonia and is treated as such, often without further investigation. But in a study published in 2016, researchers found Legionella in 1.2% of the 1,805 patients with severe respiratory illness they tested.
Legionella does well at temperatures between 37 and 42 degrees Celsius. Most healthcare authorities recommend a water temperature of 60°C or higher to ensure it can not survive.
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