People are being warned not to turn down the temperature of their hot water cylinders after a woman spent a month in intensive care with Legionnaires' disease.
The Hawke's Bay District Health Board has recently dealt with two severe cases of Legionnaires' disease, which is a severe form of pneumonia.
Tests on water temperature of the victims' hot water cylinders found one to be only 52°C.
Medical Officer of Health Nicholas Jones said the woman from that home developed severe septic shock which affected her circulation and spent a month in intensive care.
Mr Jones said people should not turn down the temperature to save power.
The legionella bacteria cannot survive in water above 60°C.
Otago Medical School's head of pathology, Professor David Murdoch, said it can be hard for experts to pinpoint specific sources of the disease.
Professor Murdoch said the condition was potentially preventable, if the sources could be identified, and he was carrying out a nationwide study on the causes.
The Energy Efficiency and Conservation Authority said setting hot water cylinders to 60 °C to kill legionella bacteria would not burn people because the temperature drops before it reaches the tap.
It said water above 55°C degrees was scalding, but between the cylinder and the tap it drops about five degrees.
The authority said because solar power systems had to pass building code consents and have a back up element, they need to reach 60 °C only once a week to kill the bacteria.