How often should unused taps be flushed?
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Key points
- Flush unused taps weekly at minimum: any outlet used less than about once a week belongs on the flushing schedule.
- Flush to temperature, not to the clock: hot reaching 50°C (55°C in healthcare), cold dropping below 20°C.
- Open spray fittings gently, or remove the spray head first, because flushing a colonised outlet releases aerosol.
- Where the risk assessment sets a higher frequency, that frequency overrides the weekly baseline.
- Log every flush and keep records for at least five years: an unrecorded flush cannot be evidenced.
Unused taps should be flushed at least once a week, running both the hot and the cold until each reaches temperature: at least 50°C on the hot (55°C in healthcare) and below 20°C on the cold. Weekly is the baseline because a week of standing water is long enough for a branch to warm into the 20 to 45°C range in which legionella multiplies and to start forming biofilm.
The weekly rule comes from the treatment of little-used outlets in HSG274, the HSE technical guidance: outlets used less than about once a week are identified in the risk assessment, put on a flushing regime, and the regime is written into the scheme of control. The full method is set out in flushing little-used outlets; this page answers the frequency question directly.
Which taps go on the weekly list
The test is honest use, not appearance. Guest bathrooms, a cleaner's cupboard sink, outside taps, taps in meeting rooms used twice a month, first-aid and eyewash points, and any tap left live on a branch after a refit: if nobody can say when it was last used, it is little-used. Building the list is the same walk-through exercise as finding dead legs, and the two overlap: a permanently unused tap on a capped branch is a dead leg to remove, while a tap that is merely rarely used is a live dead leg to flush.
Weekly is the floor, not the ceiling
The written scheme of control sets the actual frequency for each outlet, and it can be higher than weekly where the risk assessment justifies it: healthcare and care settings commonly flush at greater frequency, and any outlet serving susceptible people deserves closer attention. What the scheme cannot do is quietly let a known little-used outlet drop off the list altogether. Consistency matters more than the exact interval: a weekly flush that happens every week is a control; a daily flush that happens when someone remembers is not.
How to flush without making spray
Flushing deliberately runs water through a branch that may already be colonised, so it is itself an aerosol event. Open taps gently rather than to full flow, and on spray taps remove the aerator or spray fitting first and run a plain stream. Ventilate the room where you can. Keep the outlet running until the hot stabilises at 50°C or more and the cold drops below 20°C; the temperature chart lists the targets.
Free legionella risk assessment template
A structured Word document following the five-step approach in ACOP L8. Covers risk identification, written scheme, monitoring, and records. If it isn't written down, you can't evidence it.
Follows ACoP L8 and HSG274 Part 2. Free. No spam.
Closures and empty buildings are a special case
A building that stands empty behaves like one large little-used outlet: every tap in it stagnates at once. Schools over the holidays, void properties, holiday lets between guests and offices after long closures all need more than the routine weekly flush when they come back into use, and the recommissioning steps are covered in making a water system safe after a shutdown. If a short closure is planned, a documented weekly flush throughout keeps the system turned over and avoids a larger exercise at the end.
Finally, record every flush: date, outlet, who did it, and the temperature reached, kept in a log book for at least five years. The flushing schedule belongs in the written scheme of control, which closes the loop between the risk assessment that identified the tap and the record that proves it is being managed.
Free legionella risk assessment template
A structured Word document following the five-step approach in ACOP L8. Covers risk identification, written scheme, monitoring, and records. If it isn't written down, you can't evidence it.
Follows ACoP L8 and HSG274 Part 2. Free. No spam.
Frequently asked questions
How often should unused taps be flushed?
At least once a week. Any tap used less than about once a week counts as a little-used outlet, and the standard control in HSG274 is to flush it weekly so the standing water in its branch is replaced before it can stagnate. Run both the hot and the cold through to temperature: at least 50°C on the hot (55°C in healthcare) and below 20°C on the cold.
How long should you flush an unused tap for?
Flush until the temperature stabilises, not for a fixed number of minutes. On hot, that means the water reaching at least 50°C; on cold, dropping below 20°C. When the temperature holds at the right value, the standing water in the branch has been replaced. A tap on a long branch takes longer than one near the riser, which is why a single guessed time cannot be right for every outlet.
Which taps count as little-used?
The working line is roughly one use a week. Typical little-used outlets are guest bathroom taps, a cleaner's sink, an outside tap, a tap in a rarely occupied room, first-aid and eyewash points, and any outlet left on a branch after the fixture it served was removed. If you cannot honestly say a tap is used at least weekly, treat it as little-used and put it on the flushing schedule.
Do you need to record flushing of unused taps?
Yes. A flush that is not written down cannot be evidenced, so for the purposes of showing the risk was managed, it is no control at all. Record the date, the outlet, who flushed it, and the temperature reached, and keep the records for at least five years. The flushing schedule itself should be named in the written scheme of control, listing each little-used outlet and its frequency.
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