Legionella Flushing: How Long to Run Taps and What the Rules Say

Flushing infrequently used water outlets is one of the simplest legionella control measures — but the detail matters. Run the tap for too short a time and stagnant water remains in the pipework. Flush without recording it and you have no evidence of compliance when an inspector asks.

Here is exactly how long to flush, which outlets need it, and how to document it properly.

How long to run taps when flushing

HSG274 Part 2 does not specify a single fixed duration. Instead, it states that outlets should be flushed until the temperature at the outlet stabilises and is comparable to the supply water temperature.

In practice, this means:

Outlet type	Recommended minimum flush time	Why
Taps (hot and cold)	2 minutes each *	Enough to clear standing water from most domestic pipe runs
Showers	2 minutes with showerhead attached *	Showerheads create aerosols — flush with the head on to clear the hose as well
Long pipe runs (distant outlets)	5 minutes or until temperature stabilises	Distant outlets have more standing water to clear

* These are rules of thumb for typical domestic pipe runs. Flush longer if the temperature has not stabilised — the key test is reaching supply temperature, not a fixed time.

The two-minute guideline covers most residential and small commercial properties. For buildings with long pipe runs between the water source and distant outlets, you may need to flush for longer — check the temperature at the outlet to confirm the water is now at supply temperature.

Run both hot and cold. Flushing only the cold tap leaves hot water stagnant in the hot pipework. Both must be run.

Which outlets need flushing

Any outlet not used for seven or more consecutive days is classed as an infrequently used outlet under HSG274 and must be flushed before the next use.

Common examples:

• Vacant rental properties — every tap and shower between tenancies
• Guest rooms in hotels and B&Bs — any room not occupied for a week
• Seasonal facilities — outdoor taps, summer kitchen areas, pool showers
• Unoccupied flats in HMOs — vacant units within a shared building
• Infrequently used meeting rooms — office kitchenettes, secondary bathrooms
• School buildings during holidays — all outlets in closed wings or buildings

If you have a building where some outlets are rarely used but the building itself is occupied, those specific outlets still need weekly flushing.

How often to flush

Scenario	Frequency
Outlet used daily	No flushing needed — regular use performs the same function
Outlet used at least weekly	No flushing needed
Outlet unused for 7+ days	Flush before next use
Outlet rarely used (monthly or less)	Weekly flushing schedule recommended
Building closed for extended period	Full system flush before re-opening, with temperature monitoring

For properties with outlets that are consistently underused, setting up a weekly flushing schedule is simpler than tracking individual outlet usage. Flush every unused outlet at the same time each week and record it.

How to flush safely

Flushing sounds straightforward — turn on the tap and wait. But there are specific precautions:

1. Minimise splashing. Legionella bacteria travel through water droplets (aerosols). Run taps gently rather than at full blast, and keep the outlet pointed into the basin or drain.
2. Ventilate the room. Open windows or run ventilation while flushing showers.
3. Showerheads on. Flush showers with the showerhead attached, not removed. The hose and head contain standing water that needs clearing too.
4. Check temperature. At the end of the flush, check the water temperature to confirm it has reached supply temperature — hot water above 50°C at the outlet, cold water below 20°C.

Recording flushing — what to log

ACoP L8 requires records of all control measures. A flushing log should capture:

Field	Purpose
Date and time	When the flush was performed
Outlet location	Which tap, shower, or outlet (room number + description)
Hot water flushed	Yes/No + duration
Cold water flushed	Yes/No + duration
Temperature at end of flush	Confirms water reached supply temperature
Person performing flush	Who carried it out
Notes	Any observations (discolouration, unusual smell, slow flow)

For a property with 10 outlets, recording this on paper takes 5-10 minutes per flush cycle. Across a portfolio of properties, the paperwork adds up quickly.

What happens if you skip flushing

Stagnant water is the primary condition for legionella growth. Water sitting in pipes between 20°C and 45°C for extended periods allows bacteria to multiply. When the tap is eventually turned on — particularly a shower — those bacteria are aerosolised and can be inhaled.

The risk is not theoretical. Buildings that re-opened after extended closures without proper flushing protocols have experienced legionella growth in stagnant water systems.

From a compliance perspective, flushing records are commonly requested during compliance checks. No records means no evidence of compliance, regardless of whether you actually flushed.

Building a flushing schedule for your property

The practical steps:

1. List every outlet — go room by room and record every tap, shower, and water outlet
2. Identify which are infrequently used — any outlet not used at least weekly
3. Set a weekly flushing schedule — same day each week, same person responsible
4. Record every flush — date, outlet, duration, temperature, person
5. Review the schedule when occupancy changes — new tenants, seasonal closures, building works

LegioLog's Flushing Schedule Calculator generates a recommended flushing schedule based on your building type and outlet count — including a printable checklist you can use each week.

For the full regulatory context, see our ACoP L8 and HSG274 guide.

This guide covers legionella flushing requirements under HSG274 Part 2 for England, Wales, and Scotland. This is general compliance guidance, not legal or professional advice — for site-specific flushing protocols, refer to your building's legionella risk assessment.

Sources

• HSE — HSG274: Legionnaires' disease technical guidance
• HSE — ACoP L8: Legionnaires' disease
• HSE — Managing legionella in hot and cold water systems