Importance of flushing little used water outlets

Managing legionella risk in your hot and cold water systems: let’s talk about the importance of flushing little used water outlets.

As we are coming to the end of a long hot summer, we are seeing the effects of elevated incoming cold water temperatures PLUS the additional risk of infrequently used outlets manifesting in legionella bacteria being detected in samples taken from various water systems. This combination of factors is most likely the reason for the increase in number of legionella positive samples being seen in the last 3 months. It is also likely that these factors will mean an increase in the actual number of diagnosed cases of legionnaires’ disease this year.



Why manage the risk?

Just for clarification, dutyholders, which includes employers, those in control of premises and those with health and safety responsibilities for others, must comply with legal duties in relation to legionella. The Health and Safety Executive (HSE) have provided guidance and an approved code of practice to help with this.


HSG274 Part 2 tells us: 2.4 Within hot and cold water systems, the risk areas that support growth of microorganisms, including legionella, are controllable with good design, operation, maintenance and water system management and include…where optimum temperatures for microbial growth and stagnation occur, eg dead legs, capped pipes (dead ends), infrequently used outlets.


What do we mean by infrequently used outlets?

Perhaps you have an emergency eye wash station on your premises. Or an outside tap that is used on a seasonal basis. You may have a shower room that is only really used for storage. Or an accessible WC that is only required occasionally. Consideration should be given to removing infrequently used showers and taps, but where this is not practical or desirable, implementing a flushing regime will help to reduce the risks.

Examples of infrequent use:



There may be outlets on your premises that you assume are regularly used, but in reality, the opposite may be true. In some cases where Managed Water Services have installed temperature sensors on sentinel points of the system, our customers have informed us the outlets are regularly used. In reality the data we get back form the sensors tells a different story. The images below show the difference between a sink that is not being used (figure 1) and one that is used regularly (figure 2).

This information only came to light because of the temperature sensors that were installed on the site’s water system. We have been able to inform the customer that these outlets need to be included on their flushing regime, leading to overall improved management of the water system.


Figure 1 – temperature data from a hot outlet showing infrequent use


Figure 2 – temperature data from an outlet that is being used regularly

What do we mean by flushing?

When outlets, such as taps and showers, are not in regular use, frequent flushing of these devices for the required period 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 bacteria numbers at the outlet. Where there are high-risk populations, eg healthcare and care home scenarios, more frequent flushing may be required as indicated by the risk assessment.

We recommend that the flushing is carried out until the following two factors are met:

  • The temperature of the water at the outlet stabilises and is comparable to supply water
  • All the potentially stagnant water in the pipework is pulled through*

* This is an important point as the pipework that runs to an outlet at the end of a long corridor will contain more water (and therefore need a longer flushing period) than a little used outlet(s) that is located in a room close to an area with outlets that are regularly used. If it is a long distance away, then the flushing period will have to be longer to accommodate a total system water change.

Below is the guidance offered in HSG 274 Part 2 regarding the flushing of infrequently used outlets.

HSG274 Part 2

Table 2.1: Checklist for hot and cold water systems

Service Action to take Frequency
Infrequently used outlets Consideration should be given to removing infrequently used showers, taps and any associated equipment that uses water. If removed, any redundant supply pipework should be cut back as far as possible to a common supply (eg to the recirculating pipework or the pipework supplying a more frequently used upstream fitting) but preferably by removing the feeding ‘T’


Infrequently used equipment within a water system (ie not used for a period equal to or greater than seven days) should be included on the flushing regime


Flush the outlets until the temperature at the outlet stabilises and is comparable to supply water and purge to drain


Regularly use the outlets to minimise the risk from microbial growth in the peripheral parts of the water system, sustain and log this procedure once started


For high risk populations, eg healthcare and care homes, more frequent flushing may be required as indicated by the risk assessment


Weekly, or as indicated by the risk assessment


Steps to take

  • Make sure your premises has an up-to-date Legionella Risk Assessment.
  • Ensure you have a written Legionella control scheme.
  • Consider whether all infrequently used water outlets have been identified.
  • Make sure any flushing regime is carried out and logged.
  • Continue to implement all other actions in order to comply with duties.

What is Legionnaire’s disease?

Legionnaires’ disease is a pneumonia-like disease that has an approximate 12% fatality rate. Symptoms include: muscle pains, high temperature fevers and chills, dry cough, headaches that can lead to pneumonia and diarrhoea and signs of mental confusion.

Legionnaires’ disease is caused by Legionella bacterium, a bacterium that occurs in the natural environment. When this bacterium is released in an aerosol, a shower or a spray tap for instance, it spreads out into the atmosphere and can travel a significant distance. If a person comes into contact with the infected aerosol and it is breathed into the lungs, then it can cause Legionnaires’ disease.

According to reports, there are approximately 500 cases of Legionnaires’ disease in the UK each year. There are groups of people that are more susceptible than others; Men are more susceptible than women, those over 45 years are more susceptible, those with an underlying illness or addiction will also be more susceptible.

Need some support or guidance?

If you have any concerns about the flushing regime or other elements of legionella control for your water systems, then do not hesitate to contact us at Managed Water Services for support and guidance.

  • Contact your MWS account manager
  • See the Knowledge Library or FAQs on our website
  • Give us a call – North: 01422 208 518 / South: 01245 362 366