--- title: Legionella Risk Assessment & TMV Water Safety Guide description: TMV management guide covering Legionella Risk Assessments, stagnation risks, scalding prevention, and compliant water safety governance. image: https://www.waterhygienecentre.com/hubfs/20260520_JP%20TMV%20Images%20(6)_11zon.jpg --- [![Water-Hygiene-Centre-Logo1-2](https://www.waterhygienecentre.com/hs-fs/hubfs/Water-Hygiene-Centre-Logo1-2.png?width=225&height=80&name=Water-Hygiene-Centre-Logo1-2.png "Water-Hygiene-Centre-Logo1-2")](https://www.waterhygienecentre.com/) [![white-logo](https://www.waterhygienecentre.com/hs-fs/hubfs/WaterHygieneCentre-2019/Images/white-logo.png?width=198&height=69&name=white-logo.png "white-logo")](https://www.waterhygienecentre.com/) - [** ](https://www.facebook.com/sharer/sharer.php?u=https://www.waterhygienecentre.com/blog/tmv-legionella-risk-assessment&title=Legionella%20Risk%20Assessment%20&%20TMV%20Water%20Safety%20Guide&picture=https://2896031.fs1.hubspotusercontent-na1.net/hubfs/2896031/20260520_JP%20TMV%20Images%20%286%29_11zon.jpg&description=TMV%20management%20guide%20covering%20Legionella%20Risk%20Assessments,%20stagnation%20risks,%20scalding%20prevention,%20and%20compliant%20water%20safety%20governance.) - [**](https://twitter.com/share?source=https://www.waterhygienecentre.com/blog/tmv-legionella-risk-assessment&text=Legionella%20Risk%20Assessment%20&%20TMV%20Water%20Safety%20Guide%20-%20https://www.waterhygienecentre.com/blog/tmv-legionella-risk-assessment) - [**](http://www.linkedin.com/shareArticle?mini=true&url=https://www.waterhygienecentre.com/blog/tmv-legionella-risk-assessment&title=Legionella%20Risk%20Assessment%20&%20TMV%20Water%20Safety%20Guide&summary=TMV%20management%20guide%20covering%20Legionella%20Risk%20Assessments,%20stagnation%20risks,%20scalding%20prevention,%20and%20compliant%20water%20safety%20governance.) # **TMV Management & Legionella Risk Assessment Guide** by [Jim Perry](https://www.waterhygienecentre.com/blog/author/jim-perry), on 21-05-2026 **![20260520_JP TMV Images (6)_11zon](https://www.waterhygienecentre.com/hs-fs/hubfs/20260520_JP%20TMV%20Images%20(6)_11zon.jpg?width=2272&height=1704&name=20260520_JP%20TMV%20Images%20(6)_11zon.jpg)** **Legionella Control — Aligning Scalding Risk, Stagnation Prevention and Governance Through Structured Risk Assessments.** ** ** Water safety compliance does not begin and end with temperature checks, logbooks or routine inspections. Effective control of Legionella, scalding risk and wider waterborne pathogens relies on informed, structured risk assessments, where [Thermostatic Mixing Valves](https://www.waterhygienecentre.com/blog/tmvs-what-are-they) [TMV, including TMT – Thermostatic Mixed Tap] management plays a central and often underestimated role. TMVs are frequently treated as standard fixtures rather than critical safety devices requiring justification, monitoring and governance. In reality, the decision to install, retain, remove or modify a TMV should always be driven by risk assessment, balancing [scalding risk](https://www.waterhygienecentre.com/blog/scald-risk-tmt-tmv) with microbiological risk.   [![New call-to-action](https://no-cache.hubspot.com/cta/default/2896031/30cae303-224d-4299-9a43-10e08bb0888e.png)](https://cta-redirect.hubspot.com/cta/redirect/2896031/30cae303-224d-4299-9a43-10e08bb0888e)   Across [healthcare](https://www.waterhygienecentre.com/free-guide-healthcare), [education](https://www.waterhygienecentre.com/blog/education-legionella) and public or commercial estates, preventable [Legionella risks](https://resources-waterhygienecentre-com.sandbox.hs-sites.com/legionella-risk-assessment-1) rarely stem from major system failures. More often, they develop gradually through overlooked design decisions, redundant outlets, poorly maintained TMVs and [low use outlets](https://www.waterhygienecentre.com/blog/little-used-outlet) or facilities that introduce stagnation into otherwise compliant systems.   This position is consistent with UK HSE guidance, where [Legionella outbreaks](https://www.waterhygienecentre.com/blog/legionella-positive-results) are rarely caused by infrastructure failure. Instead, they are typically the result of water systems that are not managed correctly, with the accumulation of unmanaged or poorly governed risk within systems that remain mechanically operational.   A minor oversight today can quickly become an incident tomorrow.   ## **Why TMV Management Matters** ** ** TMVs are primarily installed to mitigate scalding risk, particularly in environments serving vulnerable users such as healthcare settings, [schools](https://www.waterhygienecentre.com/blog/legionella-schools) and [care facilities](https://www.waterhygienecentre.com/blog/legionella-control-for-care-homes).   By blending hot and cold water to a controlled outlet temperature, they reduce the likelihood of thermal injury at the point of use.   However, from a microbiological perspective, TMVs introduce additional complexity:   Where servicing, fail-safe testing and performance verification are inconsistent, TMVs can become areas of temperature instability and [biofilm](https://www.waterhygienecentre.com/blog/what-are-biofilms-1) accumulation.   For this reason, TMVs must be understood as dual risk control devices, not a standalone scalding solution. Their use must always be justified through a combination of a [scalding risk assessment](https://www.waterhygienecentre.com/scalding-risk-assessment) and Water Safety / [Legionella risk assessment](https://www.waterhygienecentre.com/legionella-risk-assessment-l8).   Installation by default, without structured justification, increases system complexity without necessarily reducing overall risk.   ## **When TMVs Are Not Required** TMVs are often installed as a precaution rather than through risk-based decision making. They may not be required where:   ## **Removing TMVs — A Structured Approach** Where a TMV is deemed unnecessary, removal must be controlled and documented:   Removal should reduce system complexity and eliminate risk, not introduce new stagnation points or risk.   ## **When TMVs Are Required** There are clear scenarios where TMVs are essential, particularly where vulnerable users are present, which may include:   This does **not** mean that TMVs are required throughout these settings – the requirement for risk assessment remains the same.   In these settings, TMVs must be:   A TMV that is installed but not maintained is not a control, it is an unmanaged risk.   ## **Managing Underused Cold Taps** A commonly identified configuration during Legionella risk assessments is a wash hand basin supplied via a TMV-controlled blended outlet [often labelled “hot”] alongside a separate cold tap that is rarely or never used.   From a scalding perspective, this may appear appropriate. However, from a water safety standpoint, the rarely used cold outlet presents a potential stagnation point.   Low-use pipework can allow water to remain static for prolonged periods, increasing the likelihood of:   In this context, “no use” does not equate to “no risk.” It represents unmanaged stagnation within a configuration that may no longer reflect operational reality.   ## What Should Happen to the Unused Cold Tap? There are three risk-based approaches listed below:   1. [Flushing Regime](https://www.waterhygienecentre.com/blog/legionella-flushing-program) [Short-Term Control]![AdobeStock_964523216 - Flushing <100KB](https://www.waterhygienecentre.com/hs-fs/hubfs/AdobeStock_964523216%20-%20Flushing%20%3C100KB.jpeg?width=305&height=202&name=AdobeStock_964523216%20-%20Flushing%20%3C100KB.jpeg) Where removal is not immediately possible: - Implement routine flushing [typically weekly, minimum 2 minutes] - Record and monitor compliance - Document clearly within the Legionella Risk Assessment. Short-term controls such as flushing can mitigate risk, but they are dependent on consistent implementation and documented oversight. 2. Remove the Redundant Outlet [Preferred Risk Elimination] Where the tap is not required: - Remove the cold tap and associated pipework - Cap pipework as close to the branch connection as possible or piece through - Eliminate deadlegs in line with [HSG274 guidance.](https://www.waterhygienecentre.com/blog/hsg-274-part-1-2024) This removes stagnation risk at the source. 3. Redesign as a Single Blended Outlet [Best Practice Solution]![20260520_JP TMV Images (1)_11zon](https://www.waterhygienecentre.com/hs-fs/hubfs/20260520_JP%20TMV%20Images%20(1)_11zon.jpg?width=243&height=324&name=20260520_JP%20TMV%20Images%20(1)_11zon.jpg) A more robust long-term solution: - Install a single TMV-blended outlet - Remove redundant hot/cold configurations - Improve system turnover through regular use.   Longer-term, risk-based solutions may include removal of redundant outlets, capping pipework close to the branch connection to minimise deadlegs or redesigning the outlet as a single blended point to improve turnover.  These decisions should always be driven by risk assessment rather than assumption. ## **Integration with Legionella Risk Assessments** Legionella Risk Assessments must do more than identify hazards; they must drive action and reflect real world usage. They should:   All remedial actions must be:   ## **The Role of the Water Safety Plan** The [Water Safety Plan](https://www.waterhygienecentre.com/water-safety-plan) is the mechanism through which risk assessment decisions are embedded into operational control. It should include:   If an unused cold tap remains, its management must be clearly defined, not assumed.   ## **Reactive Compliance vs Engineered Risk Reduction** A recurring issue across many estates is the shift toward reactive compliance, where: - TMVs are installed without reviewing actual need. - Low-use outlets remain in place despite stagnation risk. - Deadlegs are assumed insignificant. - Maintenance regimes do not reflect system complexity.   Over time, these individually manageable issues combine to increase overall system risk.   Effective water safety management requires:   Governance must be proportionate, documented and reflective of real-world use — not historic design assumptions.   ## **Long-Term Risk Control Through Intentional TMV Strategy** TMV management is not solely about preventing scalding. Legionella control is not solely about monitoring temperature. Both require a coordinated, risk-based approach that considers:   Many enforcement actions and costly remediation programmes originate from cumulative oversight, an unserviced TMV, an infrequently or unused tap, or a poor configuration that was never revisited.   The most resilient estates are those that regularly challenge legacy arrangements and ensure every outlet/facility and every TMV remains justified.   ## **Conclusion** A wash hand basin with a TMV-controlled outlet and an unused cold tap is not a minor maintenance issue; it is a clear test of governance, design intent and risk ownership.   The key question is not:  *“Is this compliant today?”*   It is:  *“Has this TMV and outlet configuration been risk assessed to control both scalding and Legionella risk over the long term?”*   Water safety is not defined by the absence of failure; it is defined by the strength of governance***. *** *** *** Feel free to reach out if you have any questions about this blog or if you would like to [consult with one of our experts for further advice on water hygiene.](https://www.waterhygienecentre.com/contact) Editor's Note: The information provided in this blog is correct as of the date of original publication – May 2026.   © Water Hygiene Centre 2026   [![New Call-to-action](https://no-cache.hubspot.com/cta/default/2896031/ba3583be-f15a-4dcf-973b-e071ac813d2d.png)](https://cta-redirect.hubspot.com/cta/redirect/2896031/ba3583be-f15a-4dcf-973b-e071ac813d2d)   #### About the author #### [Jim Perry](https://www.waterhygienecentre.com/blog/author/jim-perry) With over 30 years of experience in water system safety, Jim really knows his stuff. He’s a specialist in water quality management and has lots of expertise in design and specification reviews. He’s worked with a variety of organisations, including NHS Trusts, Local Authorities, schools, and commercial properties. ### Related Posts ### [Education – Areas of High Legionella Risk](https://www.waterhygienecentre.com/blog/education-legionella-risk) by [Jonathan Twaites](https://www.waterhygienecentre.com/blog/author/jonathan-twaites), on 30-06-2026 Legionella risk is a subject that anyone who manages water systems needs to consider and suitably manage, whether you are involved with an office block, hospital, school, or higher education. There... [Read More](https://www.waterhygienecentre.com/blog/education-legionella-risk) ### [Legionella– What’s the risk for Children?](https://www.waterhygienecentre.com/blog/legionella-risk-children) by [Jonathan Twaites](https://www.waterhygienecentre.com/blog/author/jonathan-twaites), on 16-06-2026 If you If you follow news feeds on the topic of Legionella, then you will notice that there are several headlines relating to Legionella in our schools. 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