What is HTM 04-01?

HTM 04-01 is the healthcare-specific guidance for safe water in premises such as hospitals and care settings. Its full title is "Safe water in healthcare premises", and it is a Health Technical Memorandum published by the Department of Health and Social Care. It sets out how NHS trusts, hospitals, and other healthcare estates should design, operate, and monitor their water systems to control legionella and other waterborne organisms.

If you have read the general guidance and realised your setting is a hospital or a healthcare environment, HTM 04-01 is the stricter regime that applies to you. It does not replace HSG274 or the Approved Code of Practice L8; it builds on them. The general documents cover offices, factories, landlords, and the like. HTM 04-01 takes the same principles and tightens them, because the people inside a healthcare building are far more likely to be harmed by an infection.

HTM 04-01 is guidance, not a separate law

This is the point most people miss. HTM 04-01 does not create a new legal duty. The duty comes from the Health and Safety at Work etc. Act 1974 and the Control of Substances Hazardous to Health Regulations (COSHH), and that duty applies to every building with a water system. HTM 04-01 is the route map that shows healthcare organisations how to discharge that duty in their particular, higher-risk setting.

In practice, an NHS estate following HTM 04-01 is working to the same legal obligation as an office block following HSG274. The difference is the standard expected. Because patients may be elderly, immunosuppressed, or receiving invasive treatment, regulators and the guidance expect healthcare water safety to be managed more rigorously than a general workplace.

The three parts of HTM 04-01

The current guidance is published in parts, so that different readers can find the section relevant to them:

• Part A: Design, installation and commissioning. How new or refurbished water systems should be planned and handed over, so that risk is designed out from the start.
• Part B: Operational management. How to run and monitor the system day to day, including temperature regimes, sampling, and record keeping.
• Part C: Pseudomonas aeruginosa. Advice on controlling pseudomonas in augmented care units, including water sampling of outlets.

How it goes beyond HSG274

The headline difference is temperature. Under HSG274, hot water should reach 50°C at the outlet within one minute. HTM 04-01 raises that to 55°C at the outlet within one minute for healthcare premises, while hot water is still stored at 60°C and cold water is kept below 20°C. The higher outlet target gives a wider margin against the legionella growth range of roughly 20°C to 45°C. You can see the standard figures on the legionella temperature chart.

Because many healthcare patients are at risk of scalding, thermostatic mixing valves are fitted at outlets to blend the water to a safe temperature. Those valves sit in the danger zone themselves, so HTM 04-01 treats them as controlled assets that need their own inspection and servicing regime. Monitoring frequencies, sampling, and documentation are all more demanding than in a general building, and the guidance expects the whole approach to be captured in a written plan rather than a simple logbook. That said, the discipline of recording every reading and check still sits at the heart of it, much as it does in a legionella log book.

The Water Safety Group and Water Safety Plan

HTM 04-01 asks each healthcare organisation to run a Water Safety Group (WSG) and to produce a Water Safety Plan (WSP). The plan is a living risk-management document, based on the World Health Organization's water safety plan approach, that identifies hazards across the whole water system and sets out the controls, monitoring, and corrective actions for each one.

The Water Safety Group is the multidisciplinary team that writes, owns, and reviews that plan. It typically brings together estates and facilities, infection prevention and control, microbiology, clinical staff, and the specialist water roles described below. The group meets regularly, reviews monitoring results, and decides what to do when a reading drifts or a sample comes back positive.

Named roles: who does what

Where a general premises might simply appoint a competent "responsible person", HTM 04-01 sets out a clearer chain of named roles:

• Duty Holder: the organisation and its board, ultimately accountable for water safety.
• Responsible Person (Water): the senior manager who takes day-to-day responsibility for the written scheme and its implementation.
• Authorised Person (Water): the operational lead who carries out and oversees the practical control measures.
• Authorising Engineer (Water): an independent professional adviser who audits the arrangements and advises the Duty Holder, providing an independent check on how the water systems are being managed.

The independent audit by the Authorising Engineer (Water) is one of the features that sets the healthcare regime apart. It is a built-in second opinion that most general premises do not have.

Augmented care and pseudomonas

Augmented care describes clinical settings where patients are especially susceptible to infection from the water supply. Broadly, this covers areas where patients are severely immunosuppressed, where the skin barrier is breached, or where invasive devices are used, for example intensive care, neonatal units, transplant and haematology or oncology wards, and some renal units.

In these areas the concern is not only legionella but Pseudomonas aeruginosa, which can colonise taps and outlets and reach vulnerable patients directly. Other waterborne opportunists such as stenotrophomonas maltophilia can behave the same way, which is why monitoring in augmented care looks beyond legionella alone. Part C of HTM 04-01 therefore adds pseudomonas-specific controls, including regular water sampling of outlets in augmented care areas and prompt action where the organism is found. Where an outlet is found to be contaminated, a point-of-use water filter is a recognised interim control that protects vulnerable patients while the underlying problem is put right. This is a layer of monitoring that general premises are not expected to carry out. If you are unsure what to do about a positive result, our guide on what to do if legionella is detected sets out the general principles, though augmented care will follow the tighter pseudomonas protocol as well.

Which premises it applies to, and how it ties back

HTM 04-01 is written for NHS and healthcare estates, primarily hospitals and other healthcare facilities. General workplaces, most landlords, and ordinary care settings continue to work to HSG274 and the ACOP. As a rough guide, the more vulnerable the occupants and the more clinical the care, the more the healthcare approach in HTM 04-01 is expected. A standard residential care home usually manages legionella under HSG274, while a hospital ward providing augmented care sits squarely within HTM 04-01.

Whichever regime applies, the legal foundation is the same. HTM 04-01, HSG274, and the ACOP L8 all exist to help you meet the duties in the Health and Safety at Work Act and COSHH. Understanding which one applies to your building is the first step; keeping accurate records of your testing and temperature monitoring against the right standard is how you evidence that the controls are being carried out. For the wider picture, see our overview of legionella compliance.