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Does your Care Home always get positive results for Legionella Samples

The majority of Care Homes never experience the shock of a telephone call from AquaCert to tell them we have found legionella bacteria in their water samples. For most of these properties the legionella is eradicated after a few simple measures are applied. However, for some Care Home premises, nothing appears to work and every sample submitted returns a positive result, a situation which is far more common in the larger and older properties.  So how do you manage continuous positive legionella samples In Care Homes?

Read this guidance on how to systematically work through the various options to establish where the problem lies and the methods available to resolve the issues.

The Top 10 Reasons for Recurring Legionella

  1. Hot water storage & distribution temperatures are too low.
  2. Deadleg pipework.
  3. Rarely used outlets, vacant rooms etc are not flushed every week.
  4. Hot water return pump not working.
  5. Hot water return pipes isolated.
  6. Incorrect flexible hoses used on TMVs.
  7. Scale & corrosion debris in TMVs and strainers.
  8. Pipework which is heavily scaled or corroded.
  9. Water systems not disinfected/pasteurised after refurbishments/repairs/maintenance works.
  10. No risk assessment or written scheme of control in place.


The first and most important step is to ensure the hot water temperatures are correct.

  • Hot water should be stored at 60°C or higher. At this temperatures the bacteria is killed fairly quickly.
  • Every hot water outlet should reach a minimum of 50°C within 1 minute of running the tap (unless TMVs are fitted).

If you cannot attain these temperatures, then the property will always be at risk of legionella growth.

Related Information

  • Pasteurisation
  • Thermostatic mixing valves
  • Scale formation

Flushing Rarely Used Outlets

Legionella bacteria prefer stagnant water. Whenever there is no flow the hot water pipework will cool to allow the bacteria to grow.

Similarly, cold water pipework without regular use will warm up to the ambient temperature, (probably 23°C in Care Homes) which is suitable for steady growth.

Any outlet which is not used at least once per week should be flushed regularly – at least weekly. A proper flushing regime should part of every legionella programme.

Hot and cold deadleg pipework remaining after a wash hand basin has removed

Deadleg pipework remaining after wash hand basin removed


Where there is deadleg pipework, legionella have an ideal habitat to grow.

Some deadlegs are obvious and these can be cut back as far as possible.

Unfortunately many deadlegs are hidden beneath floorboards and inside stud partitioning.

The water in the deadlegs does not heat up during a pasteurisation and disinfectants will only penetrate a few centimetres into a deadleg, therefore the legionella bacteria are not killed. Within a few days or weeks some of the legionella bacteria will migrate to the start of the deadleg and then get swept away with the flow to infect other parts of the building again.

Related Information

  • Larger, older properties
  • Refurbished properties

Larger, Older Properties

Most old properties have undergone ‘changes of use’ during their lifetime. A typical example is …

Imagine a large building erected in 1900, it may have been the manor house for gentry or a successful businessman. It would have had lead piping, servants’ rooms and probably fed from a nearby well or stream.

In 1950 ….

The property is sold and becomes a hotel, it’s connected to a mains water supply, rooms are divided to make way for more guests. Communal toilets and bathrooms and toilets are added, but much of the original pipework remains.

In 1970

The hotel is refurbished, ensuites are added to some of the rooms.

In 1990

The hotel becomes dated and is sold again, this time to a Residential Care Home Group. Dividing walls are removed and replaced with stud partitions to increase the bed capacity. Ensuites are moved and made smaller.

In 2000

The Care Home Group is bought by a larger organisation who want to use it for both Nursing and Residential Care which requires another refit of bedrooms and plumbing. A new wing was added but the hot water was simply extended rather than replaced with a larger, modern unit.

Each time the property undergoes a ‘change’ some pipework becomes redundant and is capped off. The contractors can see numerous old pipes beneath the floorboards but are not sure what they do – so they are left just in case they are important. Over time the number of deadlegs increase but they are all out of sight.

We all know how Health & Safety standards get tighter each year, nowadays legionella testing is one of the requirements. This wouldn’t have been the case just 10 years ago.

Once legionella bacteria get into a large, old property – it is almost impossible to eradicate them completely. Instead the risk has to be managed.

Refurbished Properties

Successful Care Homes often wish to expand, common ways of doing this are buying the house next door and knocking through or adding extensions.

All refurbishments will require the water supplies to be isolated for days or weeks whilst the works are in progress. Pipework which is isolated can stagnate and allow legionella bacteria an ideal opportunity to proliferate. If the plumbers leave a deadleg or do not disinfect before putting the water supplies back into service, then your new extension is contaminated with the bacteria from straight away.

When budgets are squeezed during the extension it’s not uncommon for the existing hot water supply to be extended instead of being replaced with a correctly sized unit.
If the hot water cylinder/calorifier cannot cope with the extra demand, then the correct temperatures will not be achieved and legionella bacteria will not be killed.

Thermostatic Mixer Valves (TMVs)

Another aspect of Health & Safety is the risk of scalding, especially as the sensory perception for heat recedes with age. To prevent scalding a TMV (mixer or blending valve) is installed to reduce the hot water temperature to a safe level.

These valves are installed to wash hand basins, sinks, baths & showers. For wash hand basins the typical blended temperature is 41°C which is an ideal temperature for legionella to grow.

To minimise the risk of legionella growth Thermostatic mixing valves should be sited as close as possible to the point of use. Ideally, a single TMV should not serve multiple tap outlets but, if they are used, the mixed water pipework should be kept as short as possible. TMVs should not be used with low-volume spray taps in buildings with susceptible populations.

Flexible Hoses

Flexible hoses connecting wash hand basin taps to water supply

Flexible hoses connecting WHB taps to water supply

Many TMVs are installed using flexibles rather than hard copper pipe.

If these flexibles are old, they may have EPDM or nitrile rubber components which can encourage legionella growth.

If flexibles are used then they should conform with BS6920: Parts 1 to 3.

Scale in pipework and fittings

Hard water causes scale in pipework, on showerheads and taps.

Hard scale is similar to rock and water cannot pass through it but bacteria can and do. Under a microscope scale looks like a honeycomb of caves and caverns which provide a perfect place for bacteria to live.

Hot water bath tap which is heavily scaled

Heavily Scaled Hot Water Tap

So if your pipes are scaled, then disinfectant will not penetrate the scale and kill the legionella. A few days or weeks later, any bacteria which approach the of the scale\water interface will be flushed downstream to colonise other parts of the water system.

A prolonged pasteurisation whereby the hot water temperature is maintained at 65°C or higher for a week or two may allow sufficient heat through the scale to kill legionella.

Pasteurisation (Thermal Disinfection)

Raising the temperature of the hot water to at least 65°C is an effective method of killing legionella. The operation needs to be carried out slowly and thoroughly, in most cases it takes several days.

The main points to remember are:-

  • Raise the thermostat on the calorifier/immersion heater to 65°/70°C and allow the unit to come up to this temperature and remain there for several hours.
  • Drain water from the base of the calorifier until it too is 65°C to ensure the whole of the cylinder is pasteurised.
  • Run one hot water outlet at a time, once it is above 65°C – continue running for a further 5 minutes.
  • Where the hot water outlet has a TMV fitted, run the tap but measure the temperature on the inlet to the TMV until 65°C is reached, again continue flushing for a further 5 minutes.
  • During peak usage such as morning baths, meal times – you may need to suspend the operation if the temperature reduces below 65°C.
  • Record the temperatures at each outlet (or pre TMV pipework) so that it is clear which outlets have been pasteurised in case the task is suspended for a while or there is a shift change-over.

Any legionella bacteria present in the short runs of pipework after the TMV will not be killed, for these short pipe runs regular flushing will help keep the numbers low. Alternatively, one or more disinfections may need to be undertaken.
Chemical Disinfection

There are several different types of disinfectant which are commonly used, each have pros and cons.
A chemical disinfectant will reach the pipework runs after any TMVs but will not penetrate deadlegs or heavily scaled pipework.

Chlorine Based Disinfectants

Chlorine, dosed at 50ppm is very effective at killing legionella bacteria in the bulk of the water. Unfortunately most legionella live in the invisible biofilm layer which coats every water pipe and chlorine doesn’t fully remove this biofilm. It is quite common for chlorine to disrupt the biofilm so fragments of it break down and are swept through the distribution pipework.
If you were to test for legionella within a few hours of a chlorine disinfection (after fully flushing all the disinfectant away) you’d probably find a much higher count since the biofilm fragments contain as much as 90% of the legionella.
The other drawback to chlorine is the disruption it causes, you cannot drink, cook or bathe in water with 50ppm chlorine. For small properties the disinfection can be timed to minimise disruption, for larger properties the operation will take all day.

Peroxide Based Disinfectants

Silver Peroxide is the most popular choice as it causes little or no disruption. The concentration at which it is used is significantly weaker than the average mouth wash. It’s also fairly good at breaking down the biofilm but in terms of killing power it’s not as strong as chlorine.

Chlorine Dioxide Based Disinfectants

These combine the best traits of chlorine and peroxide disinfectants. Not so many water treatment companies use them as they are more difficult to handle, testing the concentration in the system is trickier too.

Mixed oxidants

A new type of disinfectant is going through the regulatory process and should be available by the end of 2013. This promises to be the best disinfectant for the future. It is already used as a maintenance disinfectant rather than a ‘slug dose’ disinfectant.

Hot Water Temperature Trouble shooter

Stored Water Temperature of Hot Water Cylinder or Calorifier does not reach 60°C Check that the thermostat is correctly set.
Check that the boiler is on and its thermostat is at least 75°-80°C.
Check any immersion heaters to ensure they are working and their thermostats are correctly set.
Check if the kitchen staff leave a hot tap constantly running during prep or cleaning.
Check for faulty TMVs which may be returning cold water back to the cylinder
Check for scale build up.
Stored Water Temperature of Hot Water Cylinder or Calorifier only reaches 60°C for a few hours per day. Log the stored water temperature every hour to find out when the temperatures are at the highest and lowest.
It may be just during peak demand so that some of the activities which use hot water can be staggered to allow better recovery.
The unit may simply be too small to cope
Stored Water Temperature is 60°C but the return water is only 40°C Check that the return pump is turned on and working.
Trace back the return pipework and check if any valves have been isolated, open them up.
Trace back return pipework to find at what point there is a sudden drop in temperature.  Check the nearby pipework for faulty TMVs and ‘crossed pipes’.
Stored Water Temperature is 60°C but furthest outlets are below 50°C Check the return pumps and pipework (see above).
If the problem is only recent, has there been maintenance work done?  Have all the valves been fully opened.
If it’s a long standing problem, check the pipework insulation.
Consider installing a pumped return from these areas.

Continuous Disinfection

If the legionella problem still persists after all these investigations, the most likely cause is hidden deadlegs. Trying to find hidden deadlegs is extremely difficult since it involves removing floor covers and floorboards – it causes disruption and substantial costs.

In these cases, the best option is to ‘Manage’ the legionella problem so that the concentration of bacteria is kept at a lower enough level so as not be a risk.

The continuous dosing of a disinfectant is commonplace at most hospitals and many larger Care Homes.

It simply involves installing a water meter connected directly to a dosing pump, the meter controls the pump so that every 10 litres of water which passes through the meter the pump activates to inject a drop of disinfectant.

The continuous dosing may be into the rising mains or into the cold water feed to your hot water – this depends on where you are finding the legionella bacteria.

Shower Head Disinfection & Descaling Techniques

Legionella Testing – Indicative Sampling