water providers use disinfection measures to ensure water is potable when departing the treatment plant, but the water will ‘pick up’ impurities from the distribution system piping. By the time gets to your facility, it most likely has impurities in it – including Legionella. This, alone, does not represent a significant risk, usually. However, dirt is ‘food’ for bacteria, and the amount of bacteria and dirt in the water will have a direct influence on how the water will age and how biofilm will develop within the building systems. It is important to note that some municipalities have relatively warm water running in their mains, over 80˚F in some cases. These conditions may increase the bacterial loading of the water service and impact facility decisions regarding supplemental disinfection or point-of- entry filtration. A facility regularly experiencing poor water quality should consider point-of-entry filtration – either by using stages of bag filters, mechanical screen filtration systems, on-site- generated supplemental disinfection, or a combination of these.

Legionella in domestic cold water systems While normally below the temperature range conducive to Legionella growth, domestic cold water systems can harbor and grow Legionella if the piping is uninsulated and routed near hot water piping – be it domestic or hydronic – especially in enclosed riser chases with little or no ventilation. Under these conditions, cold water can be warmed into the temperature range in which Legionella is more likely to grow. Ice machines served with only cold

water can also be a source of Legionella contamination. They often include carbon filters to improve the water taste, but they remove any residual disinfectant that may have been in the city water. These machines have compressors that can warm the water and grow bacteria that can then be inhaled by a patient chewing the ice. The once-dormant bacteria warm up in the lungs and become reactivated. Limit the risk by: limiting the amount of Legionella present in the entire water system, regular filter replacement, and flushing of ice machine supply lines.

Legionella in domestic hot water systems Legionella prefers warm water. Domestic hot water systems that are not uniformly ‘hot’ can provide ideal conditions for waterborne pathogen growth. Hot water systems typically include storage tanks, piped distribution systems, master temperature mixing valves, sensor faucets with point-of-use mixing valves, flow control devices within faucets, and water- hammer arrestors for quick-closing valves – such as some solenoid valves used with


Legionella poses a risk to vunerable patients.

sensor faucets. Patient showers include mixing valves, hoses for hand-held wands, and spray heads. These are all places where warm water and biofilm are conducive to Legionella growth – which can then be aerosolised near sick patients via faucets and showers. Water temperatures can widely vary within domestic hot water. Storage tanks are hopefully kept hot enough (140˚F or more) to prevent bacteria growth, but uncirculated storage tanks will allow stratification of temperature layers and can still be a source of a potential risk. Also, depending on local codes and anti- scald measures, hot water may have to leave the main heating equipment at 120˚F. Even with 24/7 circulating pumps, the highly dynamic demand flows and inherent difficulties of balancing complex hot water distribution systems can result in a temperature-variation free-for-all. To further add potential risk, many

fixtures may be infrequently-used and may be located at the end of a long, uncirculated branch pipe run. ‘Hot’ water in piping serving those fixtures will cool off and may spend much of the day in the perfect temperature range for Legionella growth. If the fixture in question is in an ICU patient room, the risk of life- threatening infection is much higher than if the fixture were in a non-patient area. (e.g. staff restroom where it is unlikely to be near sick patients). For a building engineer managing

these issues, checking the temperatures of the return lines and ensuring the system is balanced properly may be necessary. Replacing old balancing valves with new thermostatically-operated balancing valves can help ensure temperatures are being maintained in the supply piping. Providing faucets with programmable flush operation for seldom

used fixtures can aid in preventing stagnation. Also, having supplemental disinfection or copper/silver ionisation treatment for the hot water system can limit biofilm formation in the piping system.

Impact of water

conservation measures Due to increased environmental awareness, some water conservation measures have resulted in lower flows through pipes and faucets. Lower flows can result in increased ‘water age’ i.e. water is sitting in pipes for longer, and it is more likely to grow microorganisms. Also, lower flow rates are more conducive to biofilm growth. In some areas, handwashing fixture

flow rates have been reduced from 2.5 g/m to 0.35 g/m. If that fixture has a hands-free sensor faucet with a mixing valve, only half of that 0.35 g/m (0.18 g/m) would be coming from the hot water system when the faucet is activated. These low flows are fine if the piping system is sized accordingly and the volume of hot water in the pipe to the fixture is minimised. However, that is a very low flow for a

standard code-minimum, one-half inch diameter supply pipe. This can be a serious problem if an older facility is renovated with low-flow fixtures, but the existing distribution piping was designed for much higher flows. Point-of-use mixing valves at sensor

faucets may be weak links in potable water systems because their internal check valves may be fouled and cold water could be flowing into the hot water system – adding to the difficulty of maintaining hot water system temperature above the Legionella growth range. Building engineers need to ensure


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