Hot water bacteria:
the simple facts
Introduction
In an effort to reduce electricity usage and save money, many South
Africans have been turning their attention to optimising the use of
electric geysers - the appliance that accounts for up to 50% of electricity
consumed in an average household. Savings have been achieved by either
switching the geyser off for long periods or adjusting the thermostat.
This led to many homeowners questioning whether these two practices
could, possibly, contribute to hot water bacteria growth in geysers,
potentially harmful to people. Eskom undertook extensive research to
ascertain the facts.
What is hot water bacteria?
Hot water bacteria, Legionella pneumphila, are bacillus shaped and non-spore forming, and survive and grow at water temperatures
ranging from 20°C to 45°C; bacteria growth is enhanced by low concentrations of iron, zinc and potassium in water, and stagnant
or low flow water areas encourage it.
In its most virulent form it can cause Legionnaire’s disease - its discovery occurred in 1976, when attendees of the American Legion
Convention in Philadelphia in the USA contracted the disease.
However, research indicated that only about 1% to 5% of people exposed to the bacteria get infected.
People contract Legionnaire’s disease through the inhalation of contaminated droplets of water which results in pneumonia-like
symptoms. Once inhaled, it enters the lungs, settles and grows in surrounding tissue.
Contraction of the disease is influenced by sex - men are more susceptible than women; age - people older than 50 are more
susceptible; addictions - smokers and people who abuse alcohol and drugs are more at risk; and existing health conditions –
immune-compromised people with Aids and/or TB are at high risk.
The symptoms:
•
Similar to flu, including
− High fever
− Chills
− Headaches
− Muscle pain
−
−
−
−
−
Dry cough
Difficulty in breathing
Diarrhoea
Vomiting
Confusion or delirium
Where is the bacteria found?
•Legionella is present in natural water environments
and soil.
•It can also be found in evaporative condensers, spa
baths and hot and cold water systems such as showers.
It can also be found in/on:
−
−
− Hot and cold water tanks.
− Warm water at temperatures between 20°C and 45°C.
− Pipes with little or no water flow.
− Slime and dirt on pipes feeding showers.
− Taps.
− Tank surfaces.
− Rubber and natural fibres in washers and seals of plumbing materials.
Water heaters and hot water storage tanks.
Scale in pipes, showers and taps.
MOHLALENG_ESKD_620/ ENG/Legionaires Fact Sheet
Eskom research findings and
recommendations:
The research conducted by Eskom involved taking water samples from a
number of sources, which included ‘hot water technology sources’ such as
electric element geysers, solar water heaters and heat pumps; and ‘actual
water sources’ such as borehole water, municipal water and storage tanks.
The water samples were then sampled at different temperature ranges and
their microbiological and chemical properties tested.
Findings:
•
•
•
Water source points currently used for drinking water contained Legionella.
Legionella is present in water in hot water systems at temperatures between
49°C and 55°C, but decreases over time when the water is kept at this temperature.
The most effective treatment against Legionella is to keep cold water cold and hot water, above 55°C.
Recommendations:
•
Water temperature in hot water tanks should be kept at a minimum of 55°C
(for heat pumps), optimally at 60°C.
• Water at the outlet points of hot water cylinders should be above 50°C
within a minute.
• Cold water should be less than 20°C.
• At each outlet point it should be below 20°C within 2 minutes of
running the water.
• Tanks should be insulated and closed.
• Shower heads and hoses should be dismantled and cleaned to
remove scaling.
• Any unit, such as a shower head not used regularly, should be flushed
and purged with water before use. Water must run freely through the
shower head with hot water for a few minutes before getting in the shower
to ensure that the shower head and pipes have been flushed effectively.
• Borehole water must be sterilised or filtered to prevent Legionella and bacteria
growth in drinking water.
Conclusion:
The incidence of contracting legionella-borne infections is
between 1% and 5% and, therefore, very low.
By taking basic precautions households can protect themselves
against the risk of water-borne bacterial infections.
Full information on Eskom’s rebates and incentives on energy
saving solutions for the homeowner – including solar geysers
and heat pumps - is available at www.eskom.co.za/idm.
Issued by Eskom Integrated Demand Management June 2012
Eskom Holdings SOC Limited Reg No 2002/015527/06
www.eskom.co.za/idm