Legionella Monitoring

Consideration should be given to removing infrequently used showers and taps and where removed, the redundant supply pipework should be cut back, as close as possible, to a common supply, eg to the recirculating pipework or the pipework supplying a more frequently used upstream fitting.

The risk from legionella growing in peripheral parts of the domestic water system, such as dead legs off the recirculating hot water system, may be minimised by regular use of these outlets. When outlets are not in regular use, weekly flushing of these devices for several minutes can significantly reduce the risk of legionella proliferation in the system. Once started, this procedure has to be sustained and logged, as lapses can result in a critical increase in legionella at the outlet. Where there are high-risk populations, eg healthcare and care homes, more frequent flushing may be required as indicated by the risk assessment.

Temperature plays an important role in controlling and managing legionella bacteria. The legionella bacteria can proliferate between 20-50°C and has even been known to grow at 54°C—with its most favoured temperature being 37°C (body temperature), which is why it can be dangerous to humans once contracted causing illness such as legionnaires disease, pneumonia, Pontiac fever, and the common cold and flu.

Temperatures must be reached within a specific timeframe, to ensure consistency in testing. This allows us to determine the frequency of use of the outlet, as well as those areas at a higher risk of stagnation.

Temperature readings should be taken from all sources of heat and from the nearest and furthest outlets of a water system. The sentinel points are monthly temperature points at the closest and farthest outlets, for example, taking temperatures for cold-water storage tanks would be taken from the nearest tap to the tank and from the furthest tap away. For heat sources, this means taking temperatures nearest and farthest from all heat sources such as cylinders, electric water heaters, boilers or other types of instant water heaters with single outlets such as showers.

Temperature timeframes

Hot temperature – 1 minute

Cold temperature – 2 minutes

Temperature guidelines

Hot outlet – 50°C (55°C in healthcare)

Cold outlet – <20°C

TMV* outlet – 38-43°C (ranges vary for showers/baths)

Scalding – 44°C

Heat sources

Cylinder and flow – 60-65°C

Cylinder return – 50°C (55°C in healthcare)

Combination water heater – 60-65°C

Boiler – 50-60°C (55°C minimum in healthcare)

Electric water heater – 50-60°C (55°C minimum in healthcare)

Instant water heater – 50-60°C (55°C minimum in healthcare)

*TMV – thermostatic mixing valve, blends hot and cold to create a reduced, non-scalding temperature. Often required for vulnerable persons and in healthcare.

Limescale, a source of nutrients for Legionella pneumophila, can be found in hard-water systems. The UK suffers from hard water due to the chalk limestone earth below the ground that finds its way into our reservoirs that supplies our mains water. Therefore, all outlets should be dismantled, cleaned, and descaled to remove limescale. This includes taps, spray heads, tank cleaning, showerheads and hoses.

Taking the temperature from the re-circulating return loop quarterly for subordinate temperatures.

An expansion vessel is a small white, blue, grey, or red tank. The white, blue, and grey vessel colours are to identify water system expansion vessels and the red is to identify heating system expansion vessels. Each vessel includes a rubber diaphragm that goes across the middle, where the bottom half of the vessel is filled with water and the top half with pressurised air. When water is heated at the heat source (like a cylinder) it may expand as much as 4%. The expansion vessel allows this expanded water (increase in water size) from the heat source (cylinder) to flow into the expansion vessel where the bottom half of the vessel (water) may push the diaphragm up into the top hair (airside) to allow for the expansion in water.

So why do we need to flush an expansion vessel? Well, there are 2 primary reasons. One the expansion vessel is a dead end, and as such does not allow water out of it and therefore encourages stagnation both inside the vessel and all the pipework leading to it from the feeding tee (branch of pipe that leads to it). Secondly, the diaphragm is made of rubber, which is a great source of nutrients for legionella.

The guidelines outline that we must flush the expansion vessel for six months to remove stagnant water from the vessel and relevant pipework.

A filters job is to cleanse the water impurities and allow for good quality water to pass by and therefore provides us with good quality water free from bacteria’s and the like. And in doing so the filter will become dirty itself. You will often see an internal filter that initially looks like a clear white tube that eventually turns brown/black with impurities over time.

Most manufacturers have given this timeframe 6 months before a filter is needed to be replaced or cleaned.

An annual review is an important part of your legionella testing and control. At this stage, your risk assessments, logbook, schematic, and other records will be reviewed by an engineer to confirm the status of your legionella control and management.

Coldwater storage tanks overall as a design will not change from year to year but the condition of the tank internally certainly can. Coldwater storage tanks are subject to poor temperatures (too hot or freeze), foreign bodies (bugs, animals), sediment (from mains), biofilm (from stagnation), wall spores (bacteria), and so on. Therefore, it is important to inspect both the internal and external conditions of a tank annually as a minimum.

Hot water cylinders are subject to continual heat changes that may increase the risk of legionella through non-compliant temperatures. They also require temperature gauges, pipe insulation, and should be purged periodically to remove any internal limescale, debris, or sediment. Cylinders are prone to limescale build-up and an inspection and drain down (purge) of the cylinder will help to remove unwanted items within the cylinder.

A combination water heater consists of a cold-water storage tank on top feeding the hot water cylinder below, hence the name combination water heater. Therefore, both the tank and cylinder inspections and servicing must take place on a combination water heater.

TMV or thermostatic mixing valves are blending valves that mix the hot and cold water to reduce the risk of scalding where temperatures are often set to 41°C, 3°C lower than the scalding starting temperature for vulnerable persons at 44°C.

TMVs are fitted with filters that protect the valve, where these filters are prone to blocking with limescale, sediment, and other matter. Therefore, a TMV should be serviced at least annually as recommended by most manufacturers. TMV servicing will often include temperature calibration, failsafe testing, and clean and disinfection of TMV parts amongst other actions where required.

Whilst you are required to undertake monthly temperature monitoring throughout the year at your sentinel points. You are also required to take the representative temperature at other points in the system to gather information on the rest of the water system. This could be made up of 10% of outlets in the system from areas you do not normally take the temperature from when undertaking monthly temperatures.

Manufacturers recommend that water softeners should be serviced annually. This often includes a regeneration process where backflow is created to remove any bacteria or otherwise within the water softener system. Additionally, a review of the brine (salt) tank and other elements will be reviewed to ensure a safe and suitable working condition.

t is recommended that legionella sampling or a legionella risk assessment is undertaken periodically or at least annually. The number of samples required will depend entirely on your water system. For example, samples should be taken from dead legs or areas of stagnation, cold water storage tanks, and all sentinel points to provide an accurate overview of the water systems condition.

There is a range of other risk systems that require more bespoke management. For more information please contact our team. Below we have a list of water systems that commonly require regular legionella risk assessments:

Ultrasonic humidifiers/ foggers

Spray humidifiers

Air washers

Emergency showers

Sprinkler and hose systems

Swimming pools/ whirlpools/ jacuzzis

Horticultural misting systems

Dental chair

Vehicle wash systems

Fountains and water features

Industrial processing water systems

Reverse osmosis

Water dispensers

Evaporative cooling systems