Most duty holders already know BS 8580-1 as the code of practice that tells you what a competent Legionella risk assessment should look like [1]. Fewer know that it has a companion. BS 8580-2:2022 covers the waterborne pathogens that sit beyond Legionella: principally Pseudomonas aeruginosa, but also non-tuberculous mycobacteria and other organisms that can colonise building water systems [2]. If you have ever asked “what about the bugs that are not Legionella?”, this is the standard written to answer that question.
This article explains what BS 8580-2 adds, who is genuinely expected to use it, and how it relates to the Legionella risk assessment you almost certainly already commission. It is general information and not medical advice; route any clinical or infection-control questions to the NHS, to UK health bodies, or to your own infection prevention team [9].
What BS 8580-2 is, and what it is not
BS 8580-2 is a voluntary code of practice published by BSI. It is not, in itself, a new piece of legislation, and it does not create a free-standing legal duty to assess every water system for Pseudomonas [2]. The legal anchors remain where they have always been: the general duties under the Health and Safety at Work etc. Act 1974 [10]and the requirement to assess risks from hazardous substances under COSHH [8]. What BS 8580-2 provides is the recognised, structured method a competent assessor follows when those duties point toward pathogens other than Legionella.
In practice it works as a sibling document to BS 8580-1. Where Part 1 frames the assessment around Legionella in hot and cold water systems, Part 2 broadens the lens to a wider group of organisms and the building features that let them establish, grow and reach a susceptible person [1][2]. The two are designed to be read together rather than as alternatives.
How BS 8580-2 compares with BS 8580-1
The clearest way to see the relationship is side by side. The table below contrasts the two parts on the points duty holders ask about most often.
| Feature | BS 8580-1 | BS 8580-2 |
|---|---|---|
| Pathogen focus | Legionella bacteria in water systems [1] | Pseudomonas aeruginosa and other waterborne pathogens such as non-tuberculous mycobacteria [2] |
| Typical premises | Almost all non-domestic buildings with water systems | Higher-risk settings, especially healthcare and augmented care [3] |
| Who typically needs it | Most duty holders and responsible persons | Healthcare estates teams and water safety groups, plus other higher-risk operators |
| Relationship to HTM 04-01 | Supports Legionella control referenced in HTM 04-01 | Supports the wider pathogen control HTM 04-01 expects in augmented care [3] |
| Legal status | Voluntary code of practice supporting statutory duties | Voluntary code of practice supporting statutory duties |
The headline difference is scope, not status. Both are voluntary codes that help you discharge the same underlying legal duties; Part 2 simply applies the method to a broader set of organisms in a narrower set of premises.
How the standard is structured
BS 8580-2 follows a recognisable risk-assessment shape, so anyone familiar with Part 1 will find their footing quickly. A few clauses are worth flagging for the responsible person commissioning the work.
Clause 5 deals with hazards and hazardous events: identifying which pathogens are credible in a given system and the conditions that allow them to grow and be transmitted, for example aerosol-generating outlets or points of direct patient contact [2, p.11]. This is where the assessment moves from a generic checklist to your actual building.
Clause 6 addresses competence and independence [2, p.11 to 12]. Assessing Pseudomonas and similar organisms typically calls for assessors who understand the relevant microbiology and the clinical context, and the standard sets expectations around the assessor being suitably competent and appropriately independent of any conflicting commercial interest.
Clause 10 covers reporting [2, p.25]. As with a Legionella assessment, the output should be a clear, prioritised, site-specific report that a water safety group or responsible person can act on, rather than a generic document. For background on how the wider pathogen picture fits together, see our overview of Legionella and other pathogens in building water systems.
Who actually needs a BS 8580-2 assessment
This is where proportionality matters. BS 8580-2 is aimed squarely at premises where vulnerable people are exposed to water, and where organisms like Pseudomonas aeruginosa carry real clinical weight. In healthcare, NHS England’s HTM 04-01 sets out the augmented-care settings, such as units treating severely immunocompromised or critically ill patients, where assessment and control of other waterborne pathogens is expected alongside Legionella control [3]. For those settings, BS 8580-2 is effectively the method of choice.
For a typical low-risk commercial office, a Part 2 assessment is generally not expected. The Legionella risk assessment under BS 8580-1 remains the priority, and the realistic exposure to Pseudomonas in an ordinary office washroom is usually low [1][2]. Between these poles sit premises that warrant a judgement call: care settings, hydrotherapy, dental, and similar environments where susceptible users and higher-risk water uses combine. To understand why these organisms behave differently from Legionella, our explainer on Legionella versus other waterborne bacteria and our piece on Pseudomonas aeruginosa in water give useful context.
It complements, it does not replace
The single most important point to hold onto is that BS 8580-2 sits alongside your Legionella risk assessment; it does not absorb or retire it. A healthcare site will commonly hold a current Legionella risk assessment aligned to BS 8580-1 [1]and a separate, complementary assessment for other pathogens aligned to BS 8580-2 [2], both feeding the same water safety plan and the same water safety group. Treating Part 2 as a substitute for Part 1 would leave the Legionella picture unmanaged, which is the opposite of what the standards intend.
A sensible sequence for most duty holders is to keep the Legionella risk assessment current and competent first, using the structure described in our guide to what a good BS 8580-1 assessment should include, then decide, on the basis of premises type and population vulnerability, whether a BS 8580-2 assessment is warranted. For a standard office that decision will commonly be “no”; for an augmented-care ward it will commonly be “yes” [3].
Frequently asked questions
Is BS 8580-2 a legal requirement?
No, not in itself. BS 8580-2:2022 is a voluntary code of practice, not legislation [2]. The legal duties that may make such an assessment necessary come from the Health and Safety at Work etc. Act 1974 and COSHH, which require you to assess and control risks from hazardous substances in proportion to the risk [10][8]. The standard gives you a recognised method for doing that where other waterborne pathogens are a credible concern.
How is BS 8580-2 different from BS 8580-1?
The core difference is pathogen scope. BS 8580-1 is the code of practice for Legionella risk assessment, while BS 8580-2 extends the same risk-assessment approach to Pseudomonas aeruginosa and other waterborne pathogens [1][2]. They share a similar structure and are intended to be used together, with Part 2 typically applying in higher-risk and healthcare premises.
Who actually needs a BS 8580-2 risk assessment?
It is principally aimed at healthcare and other higher-risk premises, especially augmented-care settings where vulnerable patients are exposed to water [3]. A typical low-risk office generally does not need one, because realistic exposure to these organisms is usually low [2]. Settings in between, such as care homes or dental practices, warrant a proportionate judgement based on who uses the water and how.
Does a BS 8580-2 assessment replace my Legionella risk assessment?
No. It complements the Legionella risk assessment rather than replacing it [2]. A site that needs both will commonly maintain a current BS 8580-1 Legionella assessment and a separate BS 8580-2 assessment for other pathogens, with both informing the same water safety plan [1][2]. Dropping the Legionella assessment would leave a significant hazard unmanaged.
Sources
- BSI, code of practice, BS 8580-1:2019 Water quality. Risk assessments for Legionella control. https://knowledge.bsigroup.com/products/water-quality-risk-assessments-for-legionella-control-code-of-practice-1
- BSI, code of practice, BS 8580-2:2022 (scope; clause 5 hazards and hazardous events, p.11; clause 6 competence and independence, p.11 to 12; clause 10 risk assessment reporting, p.25). https://knowledge.bsigroup.com/products/water-quality-risk-assessments-for-pseudomonas-aeruginosa-and-other-waterborne-pathogens-code-of-practice
- NHS England, health technical memorandum, HTM 04-01 Safe water in healthcare premises (augmented-care settings). https://www.england.nhs.uk/publication/safe-water-in-healthcare-premises-htm-04-01/
- HM Government, statutory instrument, Control of Substances Hazardous to Health Regulations 2002 (COSHH). https://www.legislation.gov.uk/uksi/2002/2677/contents/made
- NHS, condition guidance, Legionnaires’ disease. https://www.nhs.uk/conditions/legionnaires-disease/
- HM Government, primary legislation, Health and Safety at Work etc. Act 1974. https://www.legislation.gov.uk/ukpga/1974/37/contents