By the Unity Stays directors, Marcus Chong & Gadir Al-Khatib · Last updated 12 August 2026
In short: Manage legionella in a short let by flushing every outlet, hot and cold, before each arrival after a vacancy — shower head submerged to limit spray — descaling shower heads and keeping any hot water cylinder properly hot. A simple written risk assessment suffices for most domestic properties; use a competent assessor after a long vacancy or where water is stored.
Why short lets are specifically exposed
Legionella bacteria multiply in water held between roughly 20°C and 45°C, and the risk comes from inhaling small droplets — a shower is the classic route.
A tenanted property has water moving through it every day. A short let can sit unused for a fortnight in a shoulder month, then have someone take a hot shower within twenty minutes of arriving.
That is the pattern that matters, and it is more pronounced in properties that are seasonal, in second homes used occasionally, and in any property with a stored hot water cylinder rather than a combination boiler.
What a risk assessment involves
For most ordinary domestic properties this is a straightforward written assessment rather than an expensive exercise. Someone competent looks at the system and records the risk and the controls.
- The type of system — combination boiler, or a stored hot water cylinder, which carries more risk
- Temperatures — hot water stored hot enough, cold water kept cold
- Dead legs — pipework to a removed appliance or an unused outlet, where water sits still
- Outlets that are used rarely — a second bathroom, an outside tap, a shower nobody uses
- Anything that creates a spray — showers, and particularly shower heads that have not run for weeks
- How long the property stands empty, and at what times of year
The routine that actually manages it
The control is movement. Water that is used regularly is not the problem.
Flush all outlets before a guest arrives after any period of vacancy — hot and cold, for a few minutes each, with the shower head submerged in a bucket or a bag to limit spray. It takes minutes and it belongs on the changeover checklist.
Descale and disinfect shower heads periodically, because scale gives bacteria somewhere to sit. Keep the hot water cylinder at the right temperature rather than turning it down to save money in a quiet month, which is precisely when the risk is highest.
After a long vacancy
A property that has been closed for several weeks or a season needs more than a flush. That is the point at which a competent assessor is worth involving, particularly where there is a stored cylinder.
The same applies after any work on the water system, or where the property has been left with the heating off through winter.
The judgement is proportionate: a one-bed flat with a combination boiler let continuously is a low-risk system with a simple routine. A large house with a cylinder, an unused en-suite and a summer-only season is not.
A plain summary, not legal or health and safety advice. Where a system is complex or a property has been empty for a long period, use a competent assessor.