{
  "title": "Legionella control parameters reference",
  "source": "https://legionella.io/reference/",
  "updated": "2026-06-27",
  "disclaimer": "Indicative UK guidance baselines. Confirm every value against the current edition of the cited document and a competent, site-specific risk assessment.",
  "parameters": [
    {
      "id": "hot-store",
      "category": "Temperature control",
      "parameter": "Hot water storage temperature",
      "value": "≥ 60 °C",
      "context": "Stored in the calorifier / hot water cylinder",
      "source": "HSE HSG274 Part 2 (2024), “Operation and inspection of hot and cold water systems”, p.70",
      "sourceUrl": "https://www.hse.gov.uk/pubns/books/hsg274.htm",
      "note": "Store hot water hot enough that the whole vessel stays at temperature. Confirm the figure and any healthcare variation against current guidance and your risk assessment.",
      "url": "https://legionella.io/reference/#hot-store"
    },
    {
      "id": "hot-distribution",
      "category": "Temperature control",
      "parameter": "Hot water at the outlet",
      "value": "≥ 50 °C ( ≥ 55 °C healthcare ) within ~1 min",
      "context": "Sentinel hot outlets, time to reach temperature",
      "source": "HSE HSG274 Part 2 (2024), “Operation and inspection…”, p.70; healthcare 55 °C per HTM 04-01",
      "sourceUrl": "https://www.hse.gov.uk/pubns/books/hsg274.htm",
      "note": "Distributed hot water should reach the listed temperature quickly at the tap; healthcare uses the higher figure. Balance against scald risk via TMVs.",
      "url": "https://legionella.io/reference/#hot-distribution"
    },
    {
      "id": "cold-outlet",
      "category": "Temperature control",
      "parameter": "Cold water at the outlet",
      "value": "below 20 °C within ~2 min",
      "context": "Sentinel cold outlets, after running",
      "source": "HSE HSG274 Part 2 (2024), “Operation and inspection of hot and cold water systems”, p.70",
      "sourceUrl": "https://www.hse.gov.uk/pubns/books/hsg274.htm",
      "note": "Keep cold water cold. Warming of cold mains in summer or near heat sources is a common failure; confirm the target against your risk assessment.",
      "url": "https://legionella.io/reference/#cold-outlet"
    },
    {
      "id": "growth-range",
      "category": "Temperature control",
      "parameter": "Legionella growth range",
      "value": "20–45 °C",
      "context": "Water temperature where the bacterium multiplies",
      "source": "HSE HSG274 Part 2 (2024), Introduction; WHO (2011) “Water safety in buildings”",
      "sourceUrl": "https://www.hse.gov.uk/pubns/books/hsg274.htm",
      "note": "Dormant below ~20 °C, multiplies fastest 20–45 °C, killed progressively above ~50 °C and rapidly above ~60 °C. Indicative ranges.",
      "url": "https://legionella.io/reference/#growth-range"
    },
    {
      "id": "thermal-lethality",
      "category": "Temperature control",
      "parameter": "Time to kill at temperature",
      "value": "~60 °C: minutes · ~50 °C: hours",
      "context": "How quickly heat inactivates Legionella",
      "source": "HSE HSG274 Part 2 (2024), Introduction; WHO (2011)",
      "sourceUrl": "https://www.hse.gov.uk/pubns/books/hsg274.htm",
      "note": "Higher temperatures kill faster. Used as the basis for thermal disinfection; confirm dwell times against current guidance.",
      "url": "https://legionella.io/reference/#thermal-lethality"
    },
    {
      "id": "cfu-control",
      "category": "Microbiology & action levels",
      "parameter": "Legionella result: in control",
      "value": "≤ 100 CFU/L",
      "context": "Hot & cold water systems (HSG274 Part 2)",
      "source": "HSE HSG274 Part 2 (2024), “Microbiological monitoring” (para 2.123), p.86",
      "sourceUrl": "https://www.hse.gov.uk/pubns/books/hsg274.htm",
      "note": "System generally considered under control; continue routine monitoring. Indicative band: interpret with your risk assessment and a UKAS lab.",
      "url": "https://legionella.io/reference/#cfu-control"
    },
    {
      "id": "cfu-review",
      "category": "Microbiology & action levels",
      "parameter": "Legionella result: review",
      "value": "> 100 to 1,000 CFU/L",
      "context": "Hot & cold water systems (HSG274 Part 2)",
      "source": "HSE HSG274 Part 2 (2024), “Microbiological monitoring” (para 2.123), p.86",
      "sourceUrl": "https://www.hse.gov.uk/pubns/books/hsg274.htm",
      "note": "Review control measures and resample; if the majority of samples are positive, act. Indicative band.",
      "url": "https://legionella.io/reference/#cfu-review"
    },
    {
      "id": "cfu-action",
      "category": "Microbiology & action levels",
      "parameter": "Legionella result: immediate action",
      "value": "> 1,000 CFU/L",
      "context": "Hot & cold water systems (HSG274 Part 2)",
      "source": "HSE HSG274 Part 2 (2024), “Microbiological monitoring” (para 2.123), p.86",
      "sourceUrl": "https://www.hse.gov.uk/pubns/books/hsg274.htm",
      "note": "Investigate, review controls and consider disinfection. Indicative band; your risk assessment and a competent person guide the response.",
      "url": "https://legionella.io/reference/#cfu-action"
    },
    {
      "id": "cfu-cooling",
      "category": "Microbiology & action levels",
      "parameter": "Cooling tower action levels",
      "value": "≤ 100 · > 100–1,000 · > 1,000 CFU/L",
      "context": "Cooling towers & evaporative condensers (HSG274 Part 1)",
      "source": "HSE HSG274 Part 1 (2024), Table 1.11 “Comments and action levels in response to legionella analysis results”, p.47",
      "sourceUrl": "https://www.hse.gov.uk/pubns/books/hsg274.htm",
      "note": "Per HSG274 Part 1 Table 1.11: not detected/up to 100; >100 and up to 1,000 (low-level, reassess); >1,000 (act). Interpreted alongside the tower’s biocide and aerobic/dip-slide regime (Table 1.10).",
      "url": "https://legionella.io/reference/#cfu-cooling"
    },
    {
      "id": "freq-sentinel",
      "category": "Monitoring frequency",
      "parameter": "Sentinel outlet temperatures",
      "value": "Monthly",
      "context": "Nearest & furthest hot and cold outlets",
      "source": "HSE HSG274 Part 2 (2024), “Operation and inspection of hot and cold water systems”, p.70",
      "sourceUrl": "https://www.hse.gov.uk/pubns/books/hsg274.htm",
      "note": "Sentinels bracket each service at its extremes. Frequency is risk-assessment led; monthly is the common baseline.",
      "url": "https://legionella.io/reference/#freq-sentinel"
    },
    {
      "id": "freq-representative",
      "category": "Monitoring frequency",
      "parameter": "Representative outlet temperatures",
      "value": "On rotation (all over a set period)",
      "context": "A representative selection of other outlets",
      "source": "HSE HSG274 Part 2 (2024), “Operation and inspection of hot and cold water systems”, p.70",
      "sourceUrl": "https://www.hse.gov.uk/pubns/books/hsg274.htm",
      "note": "Rotate so a representative spread of outlets is checked over the period set by your risk assessment (often a year).",
      "url": "https://legionella.io/reference/#freq-representative"
    },
    {
      "id": "freq-calorifier-temp",
      "category": "Monitoring frequency",
      "parameter": "Calorifier flow & return temperature",
      "value": "Monthly",
      "context": "Hot water storage vessel",
      "source": "HSE HSG274 Part 2 (2024), “Operation and inspection of hot and cold water systems”, p.70",
      "sourceUrl": "https://www.hse.gov.uk/pubns/books/hsg274.htm",
      "note": "Record both flow and return; a low return can indicate stratification or scale.",
      "url": "https://legionella.io/reference/#freq-calorifier-temp"
    },
    {
      "id": "freq-flush",
      "category": "Monitoring frequency",
      "parameter": "Flushing little-used outlets",
      "value": "Weekly (or as risk-assessed)",
      "context": "Outlets not used regularly",
      "source": "HSE HSG274 Part 2 (2024), “Operation and inspection of hot and cold water systems”, p.70",
      "sourceUrl": "https://www.hse.gov.uk/pubns/books/hsg274.htm",
      "note": "Run little-used outlets to replace stagnant water; weekly is the common baseline, set yours by risk assessment.",
      "url": "https://legionella.io/reference/#freq-flush"
    },
    {
      "id": "insp-tank",
      "category": "Inspection & maintenance",
      "parameter": "Cold water storage tank inspection",
      "value": "Annually (typical)",
      "context": "CWST condition, lid, screens, sediment",
      "source": "HSE HSG274 Part 2 (2024), “Operation and inspection of hot and cold water systems”, p.70",
      "sourceUrl": "https://www.hse.gov.uk/pubns/books/hsg274.htm",
      "note": "Inspect condition and cleanliness; clean/disinfect if needed. Interval is risk-assessment led.",
      "url": "https://legionella.io/reference/#insp-tank"
    },
    {
      "id": "insp-calorifier",
      "category": "Inspection & maintenance",
      "parameter": "Calorifier inspection / drain-off",
      "value": "Annually (typical)",
      "context": "Internal inspection and/or drain to check for sludge",
      "source": "HSE HSG274 Part 2 (2024), “Operation and inspection of hot and cold water systems”, p.70",
      "sourceUrl": "https://www.hse.gov.uk/pubns/books/hsg274.htm",
      "note": "Check for sludge/scale at the base; frequency depends on findings and risk assessment.",
      "url": "https://legionella.io/reference/#insp-calorifier"
    },
    {
      "id": "insp-tmv",
      "category": "Inspection & maintenance",
      "parameter": "TMV service & fail-safe test",
      "value": "Per manufacturer (commonly 6–12 monthly)",
      "context": "Thermostatic mixing valves",
      "source": "HSE HSG274 Part 2 (2024), “Operation and inspection…”, p.70; plus TMV manufacturer instructions",
      "sourceUrl": "https://www.hse.gov.uk/pubns/books/hsg274.htm",
      "note": "Service, descale and fail-safe test; healthcare (HTM 04-01) and manufacturer schedules may be more frequent.",
      "url": "https://legionella.io/reference/#insp-tmv"
    },
    {
      "id": "insp-shower",
      "category": "Inspection & maintenance",
      "parameter": "Showerhead clean & descale",
      "value": "Quarterly (typical)",
      "context": "Showerheads and hoses",
      "source": "HSE HSG274 Part 2 (2024), “Operation and inspection of hot and cold water systems”, p.70",
      "sourceUrl": "https://www.hse.gov.uk/pubns/books/hsg274.htm",
      "note": "Dismantle, clean and descale; more often where scaling is heavy. Risk-assessment led.",
      "url": "https://legionella.io/reference/#insp-shower"
    },
    {
      "id": "insp-ra-review",
      "category": "Inspection & maintenance",
      "parameter": "Risk assessment review",
      "value": "No fixed expiry: review on triggers",
      "context": "The Legionella risk assessment itself",
      "source": "HSE ACoP L8 (2013), “Carrying out a risk assessment”, p.12; BS 8580-1:2019, clause 10 (risk review and reassessment)",
      "sourceUrl": "https://www.hse.gov.uk/pubns/books/l8.htm",
      "note": "Review regularly and whenever the system, its use, or the people exposed change. The \"every two years\" figure is a common prompt, not a legal expiry.",
      "url": "https://legionella.io/reference/#insp-ra-review"
    },
    {
      "id": "disinfect-chlorine",
      "category": "Disinfection",
      "parameter": "Shock chlorination",
      "value": "50 mg/L for ≥ 1 h, with ≥ 30 mg/L free residual at the end",
      "context": "Chemical disinfection of a water system",
      "source": "HSE HSG274 Part 2 (2024), “Cleaning and disinfection” (para 2.135), p.88; lower concentrations / longer contact times per BS 8558",
      "sourceUrl": "https://www.hse.gov.uk/pubns/books/hsg274.htm",
      "note": "HSG274 para 2.135: dose to 50 mg/L (ppm) for a minimum 1 hour contact, with at least 30 mg/L free residual chlorine remaining at the end; lower concentrations over longer contact times are acceptable per BS 8558. High-hazard work under COSHH; confirm against current guidance.",
      "url": "https://legionella.io/reference/#disinfect-chlorine"
    },
    {
      "id": "disinfect-thermal",
      "category": "Disinfection",
      "parameter": "Thermal disinfection (pasteurisation)",
      "value": "≥ 60 °C at every outlet, defined dwell",
      "context": "Heat disinfection of a hot water system",
      "source": "HSE HSG274 Part 2 (2024), “Cleaning and disinfection”, p.87",
      "sourceUrl": "https://www.hse.gov.uk/pubns/books/hsg274.htm",
      "note": "Raise temperature and run each outlet for the defined period; manage scald risk. Confirm temperature/dwell against current guidance.",
      "url": "https://legionella.io/reference/#disinfect-thermal"
    },
    {
      "id": "legal-hswa",
      "category": "Legal & duties",
      "parameter": "General duty of care",
      "value": "HSWA 1974, s.2 & s.3",
      "context": "Employer duties to employees and others",
      "source": "Health and Safety at Work etc. Act 1974",
      "sourceUrl": "https://www.hse.gov.uk/legionnaires/what-you-must-do/index.htm",
      "note": "The overarching duty under which Legionella control sits.",
      "url": "https://legionella.io/reference/#legal-hswa"
    },
    {
      "id": "legal-coshh-ra",
      "category": "Legal & duties",
      "parameter": "Duty to assess the risk",
      "value": "COSHH Regulation 6",
      "context": "Risk assessment for hazardous substances (incl. Legionella)",
      "source": "COSHH Regulations 2002",
      "sourceUrl": "https://www.hse.gov.uk/legionnaires/what-you-must-do/index.htm",
      "note": "The legal hook for a suitable and sufficient Legionella risk assessment.",
      "url": "https://legionella.io/reference/#legal-coshh-ra"
    },
    {
      "id": "legal-coshh-control",
      "category": "Legal & duties",
      "parameter": "Duty to prevent or control exposure",
      "value": "COSHH Regulations 7–8",
      "context": "Control measures and their use",
      "source": "COSHH Regulations 2002",
      "sourceUrl": "https://www.hse.gov.uk/legionnaires/what-you-must-do/index.htm",
      "note": "Underpins the written scheme of control and its maintenance.",
      "url": "https://legionella.io/reference/#legal-coshh-control"
    },
    {
      "id": "legal-notify-tower",
      "category": "Legal & duties",
      "parameter": "Notify cooling towers to the local authority",
      "value": "Required (Notification Regulations 1992)",
      "context": "Wet cooling towers & evaporative condensers",
      "source": "Notification of Cooling Towers and Evaporative Condensers Regs 1992",
      "sourceUrl": "https://www.hse.gov.uk/legionnaires/what-you-must-do/duties.htm",
      "note": "Notifiable devices must be registered with the local authority (and de-registered when removed).",
      "url": "https://legionella.io/reference/#legal-notify-tower"
    },
    {
      "id": "legal-riddor",
      "category": "Legal & duties",
      "parameter": "Report a workplace-linked case",
      "value": "RIDDOR (where reportable)",
      "context": "Reporting Legionnaires’ disease linked to work",
      "source": "RIDDOR 2013",
      "sourceUrl": "https://www.hse.gov.uk/riddor/",
      "note": "Certain work-related cases/exposures are reportable; check the RIDDOR criteria and public-health duties.",
      "url": "https://legionella.io/reference/#legal-riddor"
    }
  ]
}