Trying to save money on electricity bills by turning off your solar hot water electric booster could be putting your family at an increased risk of Legionnaires disease.
The Queensland government has also produced guidelines for domestic solar hot water users about Legionnaires disease which recommends that home hot water systems are kept at a temperature of 60 degrees Celsius.
There is well-documented evidence identifying that the risk of Legionella bacteria growth in domestic solar hot water systems increases when the water is stored at temperatures between 30 and 50 degrees Celsius.
This could be a problem if a home solar user switches off their electric booster to save money. In winter the water temperature of home solar water tanks may stay below 50 degrees for many days, until the booster is switched on, as a temperature of 40 degrees will provide for a hot shower.
Domestic solar hot water tanks should be heated to 60 degrees Celsius once a day, including on days when the booster is not required, as a precaution to keep the numbers of Legionella bacteria at a safe level.
Home solar hot water systems have a display on the tank that shows the current temperature, so it is easy for anyone to check the temperature.
– Margaret Puls
Queensland Health: Legionnaire’s disease information/guidelines
Research paper: Legionella bacteria and conditions for its growth and thermal disinfection in stored, pre-heated water for domestic purposes [PDF copy Legionnairs’ Desease Preheated_Water_Report] – sourced from Water Regulations Advisory Scheme, UK – via http://www.wras.co.uk
Media article: Qld Health report finds Wesley Hospital not negligent in legionnaire’s disease outbreak (ABC news via Yahoo)