Legionella in empty properties, voids and new tenancies
Voids, refurbishments and seasonal short lets all leave water sitting in pipes. Handling that well is straightforward, and it is the single most useful routine most landlords can adopt.
This guide covers what happens during a void, what to do before a new tenancy, how to flush sensibly and what to record.
The short answer
Water that sits still warms up and stagnates, so an empty property is one of the few situations that reliably increases Legionella risk in an otherwise simple domestic system.
Before a new tenant moves in, run the outlets through, pay particular attention to showers and little-used taps, check hot and cold temperatures behave as expected, and write down what you did.
There is no universal flushing duration or fixed frequency. What is appropriate comes from your risk assessment and official guidance for the system in front of you, not from a number copied off a website.
General information, not legal advice. This guide describes the position in Great Britain. Northern Ireland is regulated by HSENI, and the Republic of Ireland has a separate legal framework — see the country pages.
Why standing water matters
In an occupied property, water moves. Outlets are used daily, the hot water cycles and cold water is replaced with fresh mains supply. When the property empties, all of that stops. Water in the pipes drifts towards room temperature, which sits inside the range where Legionella bacteria multiply, and any sediment or biofilm has undisturbed time to develop.
The exposure risk arrives with the next person to use the shower.
During a void
- Decide at the start whether the property will be flushed periodically or drained down, and record the decision
- If flushing, run all outlets including showers and outside taps, hot and cold, on a regular routine
- Keep a simple dated log of each flush — date, outlets run, who did it
- If the property is drained down, plan a proper recommissioning before reoccupation rather than simply turning the water back on
- Do not turn the hot water off and leave a cylinder full of cooling water for weeks
Flushing without creating unnecessary spray
Flushing is only useful if it moves water through the whole run, including the parts nobody thinks about. It should also be done in a way that limits the aerosol you create, because a stagnant shower is exactly the outlet that produces breathable droplets.
- Remove the shower head, or submerge it in the bath or basin, before running the shower through
- Open windows and ventilate the room while flushing
- Run outlets at a steady flow rather than full blast, to reduce splashing and spray
- Work through every outlet, not just the ones nearest the door: en-suites, cloakrooms, utility sinks, outside taps
- Run both hot and cold at each outlet until the temperature stabilises
- Descale or clean shower heads and hoses that have been standing, and replace anything visibly deteriorated
Before a new tenancy
- 1
Check the assessment still describes the property
If nothing about the water system changed, a short review may be all that is needed. If a bathroom was refitted or a cylinder replaced, reassess.
- 2
Flush the system through
Work outlet by outlet as above, giving particular attention to anything that has not been used during the void.
- 3
Check hot and cold behave as expected
Confirm the cold runs genuinely cold and the hot reaches the expected temperature at unblended outlets, and record the readings.
- 4
Deal with shower heads
Clean, descale or replace. This is cheap, quick and removes a genuine exposure point.
- 5
Record what you did
Dates, outlets, readings and any action taken. This is the evidence that the void was managed rather than ignored.
- 6
Tell the new tenant
Explain how to use the water system, what to do after they have been away, and to report discoloured water or persistent temperature problems.
Do I need a new assessment for a new tenancy?
Not as a rule. There is no requirement for a fresh Legionella risk assessment at every change of tenant. What a changeover does provide is a natural review point — the property is empty and accessible, and you are already there.
Reassess where the system has changed, where the void was long, where works have taken place, or where the incoming household's circumstances change the risk picture.
Tracking voids in LegionellaWise
Void flushing and pre-tenancy checks can be recorded as actions against the property, with dates and photos, so the void does not become a gap in the record.
A void is one of the review triggers built into the guidance in the product, so a property returning to occupancy after a long empty period prompts you to look again rather than relying on the last report.
Questions landlords also ask
How long can a property be empty before Legionella is a concern?
There is no single threshold, and any figure presented as universal should be treated with caution. Risk builds gradually with stagnation, so a week matters far less than a month, and warm weather matters more than cold. Let the risk assessment set the routine for your property.
How long should I run each outlet when flushing?
Long enough for the temperature to stabilise and for the standing water in that run to be displaced — typically a few minutes per outlet in a domestic property. Avoid quoting a fixed number as if it were a rule; tie the approach to the assessment and to official guidance.
Should I drain the system down instead?
Draining down can be sensible for a long void or over winter, but it must be paired with a planned recommissioning. A partially drained system that still holds water in low points can be worse than one that is flushed regularly.
What should I tell a tenant going away for a month?
Ask them to run all the taps and the shower through when they return, keeping spray to a minimum, and to let you know if anything looks or smells unusual. Put it in the welcome information so it is not a one-off conversation.
See whether guided self-assessment fits your property
The free suitability check asks a short set of questions about the water system, the building and the occupants, then tells you plainly whether guided self-assessment looks appropriate or whether the property should go to a specialist.
Official sources
- HSE — Legionella and landlords' responsibilities
- HSE — Identify and assess sources of risk
- HSE — Hot and cold water systems
- HSE — Approved Code of Practice and guidance L8
General information, not legal advice. Requirements and guidance differ between jurisdictions — check the country page that applies to your property.
Related reading
How often to review
There is no statutory annual or two-yearly renewal for domestic lettings. What periodic review and event-based triggers actually mean.
How to do the assessment
A step-by-step process for a simple domestic property, from competence and system description through to findings, tenant information and review triggers.
Combi boiler properties
No stored hot water usually lowers the risk, but it does not remove the duty to assess — or the risks from stagnation, showers and little-used outlets.
Water temperatures
Common HSE reference points for hot and cold water, what a reading does and does not prove, and how to record one properly with TMV and scalding caveats.