One man has died and 16 people are in a critical condition in hospital following an outbreak of Legionnaires' disease.
A further 15 suspected cases are being investigated in Edinburgh, NHS Lothian said.
The health board said the patient who died was in his 50s and had underlying health conditions. He was being treated at the Royal Infirmary of Edinburgh.
Fourteen men and two women aged between 33 and 74 are in a critical condition with the disease and are being treated in intensive care in hospitals in the Lothian area. One man has recovered and has been discharged.
A further 10 men and five women are also being treated in hospitals but their illness has not yet been confirmed.
The majority of the confirmed cases are linked geographically to the Dalry, Gorgie and Saughton areas in the south west of the Scottish capital.
Dr Duncan McCormick, consultant in public health medicine and chairman of the incident management team, said: "I would like to express my sincere condolences to the family of the patient that died.
"Investigations into the possible source of this outbreak are on-going. Meanwhile, medical staff have been actively identifying possible cases to allow us to ascertain the full extent of this outbreak.
"I would like to reassure the public that household water supplies are safe and that Legionnaires' disease cannot be contracted by drinking water.
"Older people, particularly men, heavy smokers and those with other health conditions, are at greater risk of contracting the disease. I would urge anyone who develops symptoms of Legionnaires' disease to contact NHS 24 or their GP."
The health board said Legionella bacteria is commonly found in sources of water, such as rivers and lakes.
The bacteria can end up in artificial water supply systems, including air conditioning systems, water services and cooling towers.
Legionnaires' disease is contracted by breathing in small droplets of contaminated water.
Symptoms include mild headaches, muscle pain, fever, a persistent cough and sometimes vomiting and diarrhoea, and can begin any time between two and 14 days after exposure to the bacteria. The first case was identified on Thursday May 28.
About half of those who contract the disease will also experience changes to their mental state, such as confusion.
The condition is not contagious and cannot be spread directly from person to person.
The source of the outbreak continues to be investigated by officials from the City of Edinburgh Council's Environmental Health Department and the Health and Safety Executive.
Samples have been taken from four cooling towers in the south west of the city, though it may be up to 10 days before results are available as Legionella is a difficult bacteria to culture.
Those responsible for maintenance at the cooling towers have been advised to carry out additional chemical treatment to the water in the cooling systems as a precautionary measure.
However, the health board said other possible sources are not being ruled out.
Bacteriology expert Professor Hugh Pennington said it can be hard to trace the source of a Legionnaires' outbreak.
He told BBC Radio Scotland: "Essentially it is a preventable disease. Industrial water cooling towers are quite a common source of the bug. The bug lives in warm, fresh water.
"Basically what should be done is disinfectant should be put in the water to basically stop the bug growing.
"Well, clearly that hasn't happened and the aerosol of water that comes out of these cooling towers contains the bug, people breathe it in and then they get Legionnaires' disease which is essentially a very, very severe pneumonia, particularly affecting people who already have weakened lungs through previous disease or immune-suppressed or elderly, so because it's aerosol it can spread on the wind and that's one of the reasons why it's quite difficult to track down a particular source.
"If there are several water cooling towers in an area you have to look at them all and find out which is the source of the bug."