Legionella Written Scheme

L8 and HSG 274 describe the requirements for a Written Scheme as including:

  • purpose;
  • scope;
  • risk assessment;
  • management structure:
  • dutyholder;
  • responsible person(s) and communication pathways;
  • training;
  • allocation of responsibilities, ie to the dutyholder, responsible person(s) and water treatment service provider;
  • up-to-date schematic plan showing the layout of the system(s) and its location within and around the premises – this should identify piping routes, storage and header tanks, calorifiers and relevant items of plant, especially water softeners, filters, strainers, pumps and all water outlets;
  • the correct and safe operation of the system;
  • precautions in place to prevent or minimise risk associated with the system;
  • analytical tests, including microbiological testing, other operational checks, inspections and calibrations to be carried out, their frequency and any resulting corrective actions;
  • remedial action to be taken in the event that the scheme is shown not to be effective, including control scheme reviews and any modifications made;
  • health and safety information, including details on storage, handling, use and disposal of any chemical used in both the treatment of the system and testing of the system water;
  • incident plan, which covers the following situations:
  • major plant failure, e.g. chemical system failure;
  • very high levels or repeat positive water analyses for legionella;
  • an outbreak of Legionellosis, suspected or confirmed as being centred at the site;
  • an outbreak of Legionellosis, the exact source of which has yet to be confirmed, but which is believed to be centred in an area which includes the site.

In my experience if a Written Scheme is reviewed by regulatory agencies then one area they focus on is the remedial actions to be taken in the event that the scheme is shown not to be effective. This effectively means creating a series of “what ifs” to describe what you will do in the event something in non-conforming on site.

“What-ifs” to consider

Some simple “what ifs” will be:

  • Cold water greater than 20oC at an outlet
  • Cold water within the cold water storage tank greater than 20oC
  • Hot water in the calorifier less than 60oC
  • Hot water at the outlets less than 50oC
  • Return temperature to the calorifier of less than 50oC
  • Low flow around the hot or cold water system
  • Logbook shows regular out of specification results
  • Low oxidising biocide results
  • Malfunction of dosage and control equipment
  • Legionella positive results as a result of testing
  • Testing in the event of manual dosing biocides
  • You receive a boil notice from the water undertaking

You should consider writing responses to each of these scenarios and consider some of your own. This will then allow you to be prepared in the event of an issue occurring on site so that you can manage an increased risk of Legionella proliferating.

Don’t forget in UK law you do not have to harm someone to be prosecuted, you just need to have increased the risk of Legionella proliferation, so it is better to be prepared.


If you need help preparing a robust Legionella Written Scheme (or if you are in healthcare a Water Safety Plan) then contact Collaton Consultancy Limited for expert advice using general@collatonconsutancy.com or phone to speak to an expert on +44(0)7958 124563.

1 Comment

  1. Bullet point 10: A Legionella Positive ‘because of testing’
    This could be written better in my opinion. I think I know what you’re trying to say but this implies that the ‘positive’ is the result, due to testing causing it?

    Better would be: Legionella positives as a result of testing.

    Otherwise, very good article. Informative and one that needs sharing!!

    Liked by 1 person

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