Correct design and operation of the system is the key to prevention of Legionella in tap water piping installations. Whatever the pipe material, long stagnation times and inappropriate temperatures can cause Legionella to proliferate. Under typical practical conditions, the choice between plastics and copper has no significant influence on the risk of Legionella outbreaks.
Legionnaires’ disease is an unusual and serious form of pneumonia caused by inhalation of water droplets containing the bacteria Legionella pneumophilia. These bacteria occur naturally in low concentrations in surface water and are difficult to remove completely through disinfection because the bacteria nest in other organisms.
The possibility of Legionella pneumophilia in hot and cold water systems inside any building is to be expected, although it usually occurs only in small quantities. People become infected by legionnaire’ disease when two circumstances coincide: firstly when the concentration of the bacteria in the water is relatively high and secondly, when the water becomes vaporised so that water droplets can be inhaled. This can occur for example, in cooling towers, humidifiers and showers. The most vulnerable individuals are normally the elderly or those already weakened by sickness or disease.
It is well known that Legionella occurs in all types of piping materials. The likelihood of Legionella forming in pipes in long-term service is no different whether the pipes are copper or plastic. It is the design of the system and the conditions under which it is operated that are the real influential factors.
The most important factor for the possible development of Legionella bacteria in tap water systems is the design and operation of the system. It is well known that Legionella thrives in water that is insufficiently flushed and is allowed to remain stagnant for too long between the critical temperatures (20ºC to 45ºC). Regular and thorough flushing at or above 60ºC permanently reduces the Legionella growth.
These criteria are consistently reflected in guidelines and regulations developed in many individual countries for the design, operation and maintenance for tap water systems to avoid the growth of Legionella.