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How Safe Is Your Holiday Terrace?

Both home and abroad terrace cooling is becoming more and more popular. Instagram is littered with photographs of the perfect patio, a cooling mist wafting around tables bedecked with artfully arranged cocktails, and of exotic sun-drenched,  palm-fringed beach bars with a photogenic fog. The unseasonably warm weather here in the Netherlands may have tempted you to consider a portable misting unit (prices begin at around 80 euro) or even a DIY kit for your garden from an overseas online retailer, but how do these cooling systems work, and how safe are they?

Evaporative cooling has long been used in commercial settings such as restaurants and bars to lower the temperature of the immediate surrounding area. In fact, it’s a centuries old technique, from the simple water-soaked earthenware jars found in Mesopotamia and Egypt to the elaborate fountain palaces of the Indian Shahs, such as that of Ibrahim Adil Shah II in Kumantagi. Traditional Mediterranean and Middle Eastern homes are based around a central courtyard cooled by a fountain, whilst water-soaked jaali (decorative wooden screens attached to the outer walls of a house) are still found in India.

Modern technologies use high pressure to expel the water as mist. This can be directly over the terrace in general, or as a fog creating clouds of cool air under the umbrellas.  As the water molecules evaporate into the air they need energy to change from a liquid state into a gas. This energy is drawn from the air in the form of heat  meaning that the temperature in the immediate area drops producing a cooling effect. Depending on the air conditions the temperature can drop by almost 4° Celsius (up to 30°F).



As early as 2013 ANECPLA, the Spanish Plague Control Consortium, begun issuing warnings about the health risks of such systems, especially in view of the fact that many bar and restaurant owners were unaware of the hygiene requirements. There is usually little to no information provide by the suppliers. Public awareness campaigns were rolled out in cities across Spain to highlight the risks of Legionella contamination in a bid to reduce the spread of the potentially fatal Legionnaires disease.

Legionella bacteria live and grow in water systems with temperatures of between 20°C – 50°C. They thrive at an optimum temperature of 35°C, making your summer holiday destination as attractive to them as it is to you. The bacteria live either on protozoa in the water itself, or in the biofilms coating poorly maintained equipment. The risk of bacteria being present is increased if water sources are drawn from surface supplies, such as open storage tanks or rivers, from recycled water sources, and from water stored at warm temperatures – such as hosing lying in the sun.


The most common cause of Legionellosis is the inhalation of contaminated water droplets, such as those misted in a terrace cooling system. They can cause Pontiac disease, a ‘flu-like illness, or the more serious Legionnaires disease. This has an incubation time of between 2-10 days and symptoms include headaches, fever, loss of appetite, and listlessness. Further,  patients may suffer from muscle pain, diarrhoea and confusion. The disease ranges from a mild cough to fatal pneumonia, with organ and respiratory failure. The very young, elderly, and those with compromised immune systems are most at risk, and the World Health Organisation puts the death rate for untreated, immuno-suppressed patients as high as 80%. The overall death rate worldwide is estimated to be between 5-10%.

Legionnaires disease can be prevented by proper maintenance and water treatment. Systems should be regularly cleaned and disinfected, and flushed through to prevent stagnation. Water should be heated to above 60°C or kept cold (below 20°C) to prevent bacterial growth, as not only Legionella but also E.coli and other harmful bacteria may be present and could contaminate the terrace cooling system.  Alternatively, a reverse osmosis unit can be used. This filters not only the bacteria out of the water, but also the dust-creating, corrosive minerals. Reverse osmosis produces clean water without the need for chemical additives. As a result osmosis water is used widely in humidification systems in hospitals and nursing homes, as well as in other industries.

Many businesses and hotels DO have properly maintained terrace cooling systems complete with the necessary water treatment. They can be subject to regular inspections and have Legionella Prevention Plans in place, as per the Health and Safety Regulations in numerous countries. However, as cheap, imported systems and DIY kits become more readily available on the internet, and with the lack of information on the safety and risks of atomising water, it may be worth asking yourself, just how safe is your holiday terrace?

Cumulus Nederland BV are specialists in water treatment and humidification systems. Are you planning on buying a misting unit? Contact us for more information or a free quotation.