If your building has taps, showers and a hot water heater but no cooling tower and no spa, almost everything the law expects of you lives in one document: HSG274 Part 2, the Health and Safety Executive’s technical guidance for hot and cold water systems [2]. This is the part most duty holders actually need, and the part most often skimmed.

Part 2 is not a separate rulebook. It is one of three technical parts beneath the L8 Approved Code of Practice, alongside the parts for evaporative cooling and for other risk systems [1][2]. It matters more for ordinary premises because domestic-style hot and cold water is where the foreseeable risk usually sits, and where your scheme of control will spend most of its words.

So treat this as the engine room. What follows is what Part 2 expects you to control, the trade-offs it forces, and the failure modes that pass an audit on paper while quietly going wrong.

The temperature regime is the spine, not a target to log

Part 2’s controlling idea is simple to state and hard to deliver: keep hot water hot, keep cold water cold, keep all of it moving. Legionella thrives in stagnant water roughly between 20°C and 45°C, so the whole strategy is to push the system out of that window at every point a person might draw water [4].

In practice that means storing hot water at around 60°C and distributing it so it reaches roughly 50°C at the outlet within about a minute, with cold water kept below about 20°C and reaching that within around two minutes of running [4]. Healthcare premises work to a higher distribution figure — commonly 55°C — under HTM 04-01 [12]. Treat all of these as working expectations your risk assessment confirms for your plant, not numbers to defend regardless of what the pipes are doing.

The trap is reading those figures as monitoring targets. A green tick against “50.4°C” proves the outlet was hot for ten seconds while someone held a thermometer to it. It says nothing about the calorifier that stratifies overnight or the bottom of the storage vessel sitting at 30°C. The temperature regime is the design intent of the system; the monthly reading is one thin slice of evidence that the intent is being met. on hot water temperature guidelines goes deeper on the figures.

The contested middle: TMVs, scald risk and the growth window

The most honest tension in Part 2 is one it cannot resolve for you. You must deliver water hot enough to suppress Legionella and, at the same time, cool enough at the point of use that it will not scald a vulnerable person. Those two duties pull in opposite directions, and the thermostatic mixing valve is where they collide.

A TMV blends 60°C hot with cold to deliver, say, 41°C at a basin. That blended water, and the short length of pipe and the showerhead beyond it, sits squarely in the growth range. The valve solves a real safety problem and creates a smaller microbiological one. Part 2’s answer is not to remove TMVs but to fit them as close to the outlet as possible, keep the dead volume beyond them tiny, and put them on a periodic clean-and-descale schedule [2][4].

The pragmatic call is to treat every TMV as a named asset with its own task. If you cannot list your TMVs, you cannot maintain them, and an unmaintained mixer fed by tepid water downstream is exactly the kind of detail an investigator looks for first.

Calorifiers and dead legs: the two failure modes that hide

Two things go wrong quietly, and both survive a casual temperature round.

The first is calorifier stratification. A calorifier heated only at the top can hold a cool layer at the base, below the temperature that controls the bacteria, while the flow gauge reads a comfortable 60°C. This is why Part 2 expects an annual internal inspection and attention to the drain-off temperature, not just the flow [2][4]. A vessel that looks fine from the gauge can be incubating risk in its lowest third.

The second is the dead leg: a capped spur from a removed appliance, a rarely used outlet at the end of a run, a length of pipe kept “for future use”. Water there neither moves nor holds temperature, and it seeds the rest of the system. Part 2’s preferred fix is removal, not management — cut the dead leg back to the live pipe rather than adding it to a flushing rota you will forget. Low-use outlets that cannot be removed need flushing often enough to stop them stagnating, at a frequency set by your assessment [4][5].

A field checklist for applying Part 2

Use this when you walk a hot and cold system against its scheme of control. Record a finding against each line — a value, a date or a defect — not a tick.

Hot side

  • Confirm stored hot water temperature at the calorifier flow against your scheme’s figure.
  • Check the return temperature; a cool return points to a failed pump or balancing problem.
  • Read the hot sentinel outlets — nearest and furthest on the loop — and time how long they take to reach temperature.
  • Confirm the calorifier has had its annual internal inspection and that the base drain-off was recorded.

Cold side

  • Check incoming mains and cold water storage tank temperatures against your below-20°C expectation.
  • Inspect the tank: lid, insect screen, insulation, and any sign of warming from a roof void or adjacent plant.
  • Read the cold sentinel outlets and time how long the run takes to reach temperature.

The awkward middle

  • List every TMV and confirm each is on a clean-and-descale schedule with a last-done date.
  • Identify every dead leg and blind end; flag each for removal rather than flushing where it is feasible to cut it back.
  • Confirm low-use outlets have a flushing record with a frequency justified by the risk assessment.
  • Note any outlet, appliance or pipe run that has changed since the schematic was last updated.

Expert caveats

HSG274 Part 2 describes recognised good practice for typical buildings. It is not a verdict on yours, and it does not replace a competent, site-specific risk assessment that decides which recommendations apply, at what figures, and how often you check them. The numbers above are starting expectations to confirm against your own plant and the people who use it, not fixed rules. This is compliance guidance, not legal, medical or design advice for your premises. For how Part 2 fits the wider technical guidance and the legal duty above it, see on HSG274 in practice and on the L8 Approved Code of Practice.

FAQ

What does HSG274 Part 2 actually cover compared with the other parts?

Part 2 covers hot and cold water services — storage, distribution, outlets, showers, TMVs and calorifiers — the system type in nearly every occupied building. Part 1 covers evaporative cooling such as cooling towers; Part 3 covers other risk systems like spa pools and humidifiers [2]. Most ordinary premises live almost entirely in Part 2.

How often does Part 2 expect temperature monitoring?

The general expectation is monthly checks at sentinel outlets, longer-interval checks across a representative spread of other outlets, and an annual calorifier inspection — but the exact regime is set by your risk assessment, not a fixed national timetable [4][5]. A simple, stable system may justify less; a complex or higher-risk one will need more.

No. The legal duty flows from health and safety law and the L8 Approved Code of Practice; Part 2 is technical guidance on how to meet it for hot and cold water [1][2]. Following it is the most defensible route to showing you controlled the risk, and a court can weigh an unexplained departure from it against you.

Your next move

Pick one hot water loop today and read it the way Part 2 does, not the way your logbook does: storage flow temperature, the return, the furthest sentinel outlet, and the calorifier base drain-off. If those four disagree, you have found a real control gap a tidy monthly reading was hiding. Capturing those readings — with the reason each one matters — in a digital logbook rather than a clipboard makes the next gap far easier to spot before an auditor does.

Sources

[1] HSE, “Legionnaires’ disease. The control of legionella bacteria in water systems - ACoP and guidance (L8)”. https://www.hse.gov.uk/pubns/books/l8.htm [2] HSE, “Legionnaires’ disease: Technical guidance (HSG274)”. https://www.hse.gov.uk/pubns/books/hsg274.htm [4] HSE, “Hot and cold water systems”. https://www.hse.gov.uk/legionnaires/hot-and-cold.htm [5] HSE, “Testing and monitoring your water system for legionella”. https://www.hse.gov.uk/legionnaires/testing-monitoring-water-system.htm [12] NHS England, “Health Technical Memorandum 04-01: Safe water in healthcare premises”. https://www.england.nhs.uk/publication/safe-water-in-healthcare-premises-htm-04-01/