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LEGIONELLA TESTING – HOT WATER

Legionella testing kits for hot water

The 'hot' water which supplies our sinks and wash hand basins is known as Domestic Hot Water.

There are numerous methods of generating this hot water, such as:-

  • Immersion heaters.
  • Calorifiers.
  • Electric water heaters.
  • Gas fired water heaters.
  • Combi boilers.

Some systems are pumped, some are gravity fed and others use the incoming mains pressure to send the water around the building. Larger and/or modern buildings incorporate a return system whereby the water is constantly circulated enabling virtually instant hot water when you turn on a hot water outlet.

Legionella bacteria will thrive in water temperatures between 20°C-46°C, their numbers increase most rapidly between 35°C-40°C.

Consequently the areas which are most likely to harbour this bacteria are:-

  • Rarely used outlets (which allow the supply pipework to cool down).
  • Remote areas of the building, especially in systems which do not constantly recirculate.
  • Outlets with intermittent use such as vacant rooms in Care Homes, Hotel rooms awaiting refurbishment, holiday lets etc.

AquaCert recommend that you sample the outlets where you are most likely to find the bacteria and we have developed a test kit where you can 'Bulk' up to four locations into a single sample. This means that you get four separate locations tested but you only pay for a single laboratory analysis. We can safely accomplish this since our laboratories can isolate legionella bacteria even at very low numbers, so even if only one of the four locations has just 50cfu/litre, we shall detect them (see note 1).

We don't recommend 'bulking' for showers or calorifiers.

The following table references come from HSG274

- para 2.125

Table 2.2 gives guidance on action to take if legionella is found in the water system. However, for healthcare premises with vulnerable patients, the action levels and recommended actions in Table 2.3 should be considered.

Table 2.2 Action levels following legionella sampling in hot and cold water systems

Legionella bacteria (cfu/l) Recommended actions
>100 cfu/l and up to 1000 if the minority of samples are positive, the system should be resampled. If similar results are found again, a review of the control measures and risk assessment should be carried out to identify any remedial actions necessary or if the majority of samples are positive, the system may be colonised, albeit at a low level. An immediate review of the control measures and risk assessment should be carried out to identify any other remedial action required. Disinfection of the system should be considered
>1000 cfu/l  The system should be resampled and an immediate review of the control measures and risk assessment carried out to identify any remedial actions, including possible disinfection of the system. Retesting should take place a few days after disinfection and at frequent intervals afterwards until a satisfactory level of control is achieved.

Table 2.3 Actions to be taken following legionella sampling in hot and cold water systems in healthcare premises with susceptible patients

Note 1
HSG274 has recommended action levels when the legionella concentration exceeds 100 (cfu/litre). In a 'bulked' legionella sample, AquaCert will be able to detect if this concentration exists in any of the four locations selected.

If legionella is found, we will contact to discuss the options of disinfection, thermal pasteurisation and re-sampling individual locations.

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