The Problem with Standing Water
Water that sits in pipework without flowing loses its residual disinfectant, reaches ambient temperature, and becomes an ideal breeding ground for bacteria including legionella. A single unused shower outlet can harbour enough bacteria to pose a serious health risk when finally used, because the aerosol spray delivers contaminated water directly into the lungs.
This is not a theoretical risk. Several significant legionella outbreaks have been traced to infrequently used outlets in hotels, hospitals, and office buildings. The period of building closures during 2020 highlighted the issue dramatically, with public health authorities issuing specific guidance on recommissioning water systems before reopening.
Which Outlets Are at Risk
Any tap, shower, or water-connected appliance that is not used at least weekly is considered an infrequently used outlet and requires a flushing regime. Common examples include:
- •Guest bedrooms and en-suites in hotels during low-occupancy periods
- •Washrooms in vacant office floors or unlet retail units
- •Staff showers and changing facilities used only seasonally
- •Fire hose reels and sprinkler test points
- •Outdoor taps and garden irrigation connections
- •Redundant pipework from previous building configurations
Flushing Protocols
The standard recommendation is to flush all infrequently used outlets for a minimum of two minutes at least once a week. This should include both hot and cold supplies, and the flushing should continue until the water runs at the correct temperature (cold below 20°C, hot above 50°C). Showers should be flushed with the head removed or held close to the drain to minimise aerosol generation.
For buildings with many infrequently used outlets, a structured flushing schedule is essential. Each outlet should be numbered and mapped, with a log sheet recording the date, time, and name of the person who carried out the flush. This documentation is critical for demonstrating compliance during inspections.
When Flushing Isn't Enough
If an outlet has been unused for more than a month, simple flushing may not be sufficient. Extended stagnation allows biofilm to develop on pipe surfaces, and flushing alone will not remove established biofilm. In these cases, the pipework may need to be chlorinated before the outlet is returned to service.
For outlets that are permanently unused, the best approach is to remove them entirely and cap the pipework, eliminating the dead leg. If removal is not practical, consider installing automated flushing devices that periodically discharge water to maintain flow. Your risk assessment should identify all infrequently used outlets and specify the appropriate management strategy for each.