Flushing drinking water systems properly – why it matters

Flowing drinking water helps maintain the quality of the installation. When water remains stagnant in the drinking water system for several hours or even days, its quality can deteriorate.

During stagnation:

• Microorganisms and bacteria that were originally present in harmless quantities can multiply to levels that may pose a health risk.
• The temperature and oxygen content of the water can change, creating favourable conditions for microbial growth.
• Biofilm can develop on the inner surfaces of the pipes if water remains static for an extended period. Within this slimy layer, bacteria find ideal conditions to reproduce. Deposits and dissolved nutrients can further promote biofilm formation. In particular, Legionella pneumophila and other waterborne bacteria can proliferate significantly.

That is why the basic rule applies: “Drinking water must flow!”

Recommendations for flushing drinking water systems

Water should be completely exchanged at least every 72 hours.

As a general rule, flushing should continue for at least four minutes once a stable temperature has been reached.

These recommendations are based on UK guidance such as the HSE Approved Code of Practice (ACoP L8) and HSG274 Part 2, which provide practical advice on controlling the risk of Legionella in hot and cold water systems.

The operational burden of flushing

The difficulty lies in implementation. Manual flushing programmes rely on people, and people work in real organisations under real pressures. Staff need clear responsibility, sufficient time, access to outlets, reliable records, and a process that can actually be sustained week after week. In a large estate, that is no small ask.

It is one thing to say that every low-use outlet should be flushed at the required interval. It is another to achieve that consistently, for example across a changing hospital footprint with competing priorities, staffing constraints, refurbishments, and intermittent service disruption.

This is not an argument against flushing. It is an argument against pretending that flushing is easy.

In practice, the more complex the estate, the more important it becomes to distinguish between policy and dependable delivery. A flushing regime is only as good as its execution. Where manual regimes are difficult to sustain, additional support may be needed if organisations want the control measure to be more than aspirational.

Automated flushing systems as support

That is where automated support can enter the conversation in a reasonable, non-dramatic way. 

Automated flushing devices, such as the compact and self-sufficient FLUSH 2.0 system, also offer effective preventive protection against stagnation.

In areas with persistently low use, temporary closures, phased openings, or awkwardly located outlets, automated flushing can help maintain turnover more consistently than a regime that relies entirely on busy teams remembering and recording every action. Used well, it is not a substitute for good system design; it is a practical way of supporting intended operation where the estate itself makes consistency difficult.

Recommendations for domestic users

Private users can also follow this recommendation: after a longer period of absence – for example after a holiday or a weekend away – it is advisable to let all taps run in accordance with the flushing guidance.

This applies not only to households, but also to motorhomes and caravans: if the vehicle has not been used for some time, water can stagnate in the pipes and storage tank. Therefore, all pipes should be thoroughly flushed after each period of non-use, and the fresh water tank should be emptied and cleaned regularly. This helps to ensure hygienically safe drinking water even when travelling.

Tap and shower filters – additional protection in case of hygiene risks

Regular flushing is a key measure to prevent stagnation and maintain drinking water hygiene.

In certain situations, however, flushing alone is not sufficient – for example in cases of existing contamination, after refurbishment work, or in buildings with older pipework.

In such cases, tap and shower filters provide an effective additional layer of protection: they reliably retain bacteria and therefore reduce the risk of potential health hazards.

In sensitive environments such as hospitals, care facilities or nurseries, they are an established preventive measure.

But even in domestic settings, water filters can provide added protection until the drinking water quality has been fully restored on a permanent basis.