Legionella Monitoring

Most taps are used weekly if not daily, which helps to keep water moving making it difficult for bacteria to settle and grow. However, in commercial settings, many outlets are seldom used if at all. Examples might include office showers, school changing room showers, accessible toilets, and bib taps. Stagnation is arguably the number 1 cause for legionella proliferation, and therefore plays a vital role in your legionella control and management.

All infrequently used outlets should be flushed every 7 days (or twice weekly in healthcare) to ensure water does not stagnate and encourage legionella growth. Outlets should be flushed until a stable and compliant temperature is reached.

Knowing what outlets are infrequently used – there are 2 good indicators to tell us what outlets need to be added to the weekly flushing regime. Number 1 – you know you do not use the outlet. If it’s rarely used or an unoccupied area, it should be put onto the weekly flushing regime. Number 2 – non-compliant temperatures. If your outlet is not reaching the desired temperature range within the allowed timeframe when most other outlets do, this indicates that the outlet may be infrequently used and should be placed onto the weekly flushing regime.

Temperature plays an important role in legionella control and management as the bacteria can proliferation between 20-50°C and has even been known to grow at 54°C, with legionella’s 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. This allows us to ensure temperature testing remains consistent and allows us to determine frequency of use of the outlet and potential areas of stagnation or risk.

Temperatures are required to be taken from all heat sources and the sentinel points of a water system. Sentinel points are the monthly temperature points at the nearest and furthest outlets of each water system. For example, taking the sentinel points from a cold-water storage tank would consist of taking temperature from the nearest tap to the tank and the furthest away. For heat sources this means taking the temperatures nearest and furthest from all heat sources. This may be a cylinder, electric water heater, boiler or otherwise. However, in the case of an instant water heater with a single outlet such as a shower, the outlet becomes the nearest and furthest so one temperature would be all that can be taken.

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 is a great source of nutrients for legionella. Limescale can be found anywhere in a water system where there is hard water. 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 the presence of limescale. This includes taps, spray heads, and shower heads and hoses.

Regularly testing your closed heating or cooling system for microbiological and chemistry levels ensures your system is under control and is a preventative task that helps reduce risk of system failure, corrosion, scale, poor flow and bacterial growth. All of which can help reduce large bills to repair inevitable system failures if no testing is carried out. Such testing can help identify sufficient chemical inhibitor levels such as Molybdate and Nitrite. 

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 (air side) 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 pipe work 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 to legionella.

The guidelines outlines that we must flush the expansion vessel six monthly 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 overtime.

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 control. At this stage your risk assessment, logbook, schematic, and other records will be reviewed by an engineer to confirm the status of your legionella control and management.

Cold water storage tanks overall as a design will not change from year to year but the condition of the tank internally certainly can. Cold water 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 condition 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 a 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 that 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 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 temperature from when undertaking monthly temperatures.

Manufacturers recommend that water softeners should be serviced annually. This often includes a regeneration process where a back flow 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.

It is recommended that legionella sampling 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 are a range of other risk systems that require more bespoke management. For more information please contact our team. Below we have a list of common other risk systems:

• 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
• More