The bacterium Legionella, ubiquitous in waters in the natural environment and in man-made water systems, can cause a form of pneumonia and its presence in domestic water systems needs to be managed effectively to avoid nosocomial infection, therefore.
Legionella survives in temperatures between 5° and 60°C, but is most prolific in the 20° - 45°C range. Thermal disinfection is the recognised means for killing Legionella and other bacteria and therefore DHWS are generally maintained at 60°C and above. The raised temperature also serves to increase the total hot water capacity of the system. The cold water system should be maintained below 20°C to prevent multiplication of any organisms present in the water.
Hot water circulating at 60°C, however, poses a scalding risk and hence the hot and cold water supplies should be mixed close to the outlet manually or by a thermostatic mixing valve (TMV), which accurately proportions the amounts of hot and cold water to provide blended water at a safe set temperature.
The deadleg is the section of pipe between the outlet and the point where the two water supplies meet. When not in use, the water held in the deadleg will cool to the ambient temperature (> 20°C), thus providing favourable conditions for Legionella growth. This risk must be managed, therefore. The deadleg should be minimised as far as possible and turnover of water increased to reduce stagnation. Infrequently used outlets need to be flushed out regularly to combat stagnation.
System design and routine maintenance is therefore of paramount importance and should also include regular flushing of the pipework to clear any biofilm that may have become established on the inside surface of the pipes.
The Optitherm Thermostatic Tap has been specifically designed to reduce the potential for Legionella growth. The integral thermostatic mixing valve is immediately upstream of the outlet, which means that the mixed water deadleg is practically eliminated. It is also a combined thermostatically controlled hot tap and a dedicated cold tap. Therefore, every usage – be it for warm or cold water delivery – will draw cold water through to the outlet, reducing stagnation. A combined 6l/m flow regulator and conditioner is integral to the outlet and ensures the water flows as an even steady column into the basin with no splashing or aerosol creation.
Routine maintenance of the tap and also the hot and cold water systems is very simple and straightforward, while minimising disruption to the delivery of healthcare. A flushing kit can be used, in-situ, for water supply sample collection and also for routinely flushing the pipework. These features all improve the manageability, thus reducing the risk, of waterborne pathogens such as Legionella and Pseudomonas from becoming an infection risk.
