Legionella in a block of flats: who is responsible for the communal water, what HSE says to measure, and what a monthly round adds up to

A leaseholder writes to the managing agent: "My flat has a shower I hardly use. Is the building checked for Legionnaires' disease?" The block has a cold water tank in the roof, a central hot water cylinder in the plant room and a run of pipes to 30 flats. Which of them is the agent's business, and what should the file hold?

Who holds the duty

HSE's page on what you must do says that as an employer, or someone in control of premises (including landlords), you are responsible for health and safety. The duties it lists are to identify and assess sources of risk, manage and prevent or control the risk, and keep and maintain the correct records. The page does not use the term "responsible person".

HSE's separate page for landlords defines a landlord as anyone who rents out a property they own under a lease or a licence shorter than 7 years. That definition fits an owner who lets a flat on a short tenancy. A flat held on a long lease sits outside it, so for the shared parts of a block the wording that matters is "someone in control of premises". The party that controls the tank, the cylinder and the common pipework is normally the freeholder, the residents' management company or the right to manage company, with the managing agent acting under the management agreement. The lease and the agreement say who arranges it; where they are silent, ask the insurer and take advice. The HSE landlord page itself does not discuss shared systems in blocks.

The three numbers

HSE's page on hot and cold water systems gives the figures to measure against:

• Hot water stored: at least 60C.
• Hot water at the outlet: reaching 50C within 1 minute (55C in healthcare premises).
• Cold water: below 20C, where possible.

The same page gives no monitoring frequency for little-used outlets. It points to HSE's technical guidance, HSG274, for how often to inspect, monitor and flush. HSE's landlord page adds that the law does not prescribe a review every year or every two years: the risk assessment should be reviewed periodically, especially when the system changes. It also says there is no legal requirement for a "legionella test certificate". HSE presents temperature monitoring as a reliable way to confirm that the system is under control.

What a round adds up to

Say the assessment names these check points for one block: the hot water store, the cold tank and four sample outlets (the furthest flat on each riser and two others). That is 6 readings per round.

The monthly interval is our assumption for the count. The assessment, and HSG274, set the real interval for each check, and some are less frequent. The point of the arithmetic is the volume: across ten blocks, hundreds of figures a year each need a date, a name, a comparison with 60C, 50C or 20C, and a reaction if one is out.

Little-used outlets

HSE describes a dead leg as a pipe leading to an outlet which water flows through but the outlet is unused or rarely used. In a block, that includes a flat that has been empty for months, a spare outside tap, or a pipe left behind after works. A flat's own taps and shower are the occupier's, but the shared pipe that serves them is the building's. Note which flats are void in the file.

What the file should hold

1. The written risk assessment, with its date and the name of who did it.
2. A schematic or list of the system: tanks, cylinders, pumps, risers, and the check points.
3. Dated temperature readings against the three figures.
4. What was done when a reading was out of range, and the date it was put right.
5. The date for the next review, and the reason it is set there.
6. A list of void flats and what was done with their water.

For the rest of the compliance calendar, our readiness check lists the items an auditor will ask for, the asbestos duty to manage guide covers another survey duty on the common parts, and the four-question guide to fire and building safety duties sorts out which other rules apply to a particular building. If remedial work to a tank or cylinder is large, check section 20 consultation first.

Overlyft builds AI staff who join a block management team: they take each round of readings as it is sent in, compare every figure with 60C, 50C and 20C, flag the ones out of range and write the file note and the contractor instruction for the property manager to approve, so the team is ready for the volume that a portfolio brings.

This is general information, not legal or health and safety advice. Ask a competent water hygiene assessor about each building.