How often should a shower not in use be run?

A shower that is not in regular use should be run 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 the branch feeding the shower to warm into the 20 to 45°C range legionella grows in and start building biofilm.

The weekly figure comes from the standard treatment of little-used outlets in the HSE guidance: any outlet used less than about once a week goes on a flushing regime, and the flushing regime is part of the written scheme of control. Where the risk assessment identifies a higher risk, the frequency goes up from weekly; it never silently drops below it.

What counts as a shower "not in use"?

The working line is roughly one use a week. A guest bathroom, an ensuite in a room that is rarely occupied, a staff shower in a little-used changing room, a shower over a bath that everyone uses the taps from instead: all of these are little-used even though they look perfectly serviceable. The quickest check is to ask, honestly, when each shower was last run. If nobody can say, it goes on the weekly list. This is the same exercise as identifying little-used outlets generally, and it overlaps with finding dead legs: a shower that is never used is a live dead leg with a spray plate on the end.

How to run it: gently, and to temperature

Flushing an unused shower is itself a release of aerosol from a branch that may already be colonised, so do it gently. Where the head or hose comes off, remove it and run the water as a stream; where it does not, open the mixer slowly so the flow does not atomise, and ventilate the room. Keep the hot running until it stabilises at 50°C or more, then the cold until it drops below 20°C. Clean and refit the head afterwards; heads and hoses also need periodic descaling and disinfection, covered in cleaning shower heads.

Settings that need more than weekly

Weekly is the floor, not the ceiling. In healthcare and other higher-risk settings the water safety plan may set more frequent flushing, and any setting where susceptible people shower, such as care homes, will typically treat shower control as a priority item with tighter frequencies and closer recording. Whatever frequency your risk assessment sets, it is the consistency and the record that make it a control.

After a long closure, weekly flushing may not be enough

A shower that has stood for months, for example over a summer closure or in a void property, has stagnated through its entire branch, not just the last metre. Before it goes back into use, flush the whole system through to temperature, clean and disinfect the head and hose, and where the risk assessment flags it, disinfect or sample rather than relying on flushing alone. The recommissioning steps are set out in making a water system safe after a shutdown.

Finally, write every run down: date, outlet, who ran it, and the temperature reached. A log book entry takes seconds and is the only proof the control happened. The temperature checker helps you record the readings as you take them.