How to survey a property for Legionella

What you need

One thing you must have: a digital thermometer with a probe — not an infrared one. After that it depends on the property. A tape measure, if it stores water in a tank or a cylinder. A torch, if there is a loft. And access to every room and the stop tap. Allow thirty minutes to an hour, depending on the size and type of the water system.

Legionella, briefly

Legionella is a bacterium found in mains water in very small numbers — harmless at that level. It multiplies in water held between twenty and forty-five degrees, and in water that stands still. Below twenty, it lies dormant. Above sixty, it cannot survive.

It becomes dangerous when water carrying the bacteria is breathed in as an aerosol — fine airborne droplets. A shower or a spray hose makes them most readily, but any outlet can: a running tap, even a flushing toilet. Breathing them in can cause Legionnaires’ disease, a serious pneumonia, or Pontiac fever, a milder flu-like illness. Older people, smokers, and anyone with a weakened immune system are most at risk.

Control is simple to state: keep hot water hot, keep cold water cold, keep water moving, and keep outlets clean. That is what the assessment checks.

The guidance

This survey is built in line with the Health and Safety Executive’s guidance: what it asks, and the documents it produces, follow what that guidance expects.

How to survey

The survey follows the water. In at the stop tap. Through everything that stores or heats it — tanks, cylinders, boilers, filters. Out at every tap, shower and appliance, and away through the drain. Answer in that order, and nothing is missed.

You are looking for water that stands still, and for places bacteria can get in: dead ends of capped pipework, outlets nobody uses, tanks without a tight lid, valves and filters that are never maintained, hoses left connected. Every question points you at one of these. Look properly, and answer what you see.

Think of the property as one line of water. Wherever it stops moving, wherever it sits warm, wherever something unclean can reach it — that is where the risk lives.

Using DwellFlow

One question per screen, in the same order as the water. Answer what you can see. The question mark opens help: what you are looking at, and why it matters. If you cannot answer, press “I can’t answer this” — the gap is recorded. Never guess. The Flag button is for anything you cannot identify: photograph it, add a few words, carry on.

When a photograph is asked for, it tells you what should be in the frame. Step back. Temperatures: hold the probe in the running water. For hot, record the hottest reading it reaches within a minute. For cold, the coldest within two. Type what the thermometer shows — and if a reading needs acting on, the survey tells you there and then. Everything saves as you go, with or without signal.

If you are stuck: the Ask button beneath the help answers questions about the one you are on. Otherwise, record it honestly — “I can’t answer this”, or a flag with a photograph. The full guide is behind Guide, at the top of the screen.

Before you finish, the survey is read back and anything incomplete is queried. Answer while you are still in the house. Submit, and three documents are issued: the risk assessment, the tenant sheet, and the Written Scheme of Control.