5 Common Areas of Water Stagnation in Commercial Buildings

Introduction

Water stagnation is a hidden issue in many commercial buildings — and one that can have serious consequences if overlooked. From poor water quality and system inefficiencies to the growth of harmful bacteria like Legionella, the risks are real. For facilities managers, being able to identify and prevent stagnation is not just about ticking boxes - it’s about protecting people, staying compliant, and keeping systems running smoothly.

This guide highlights the key areas in building water systems where stagnation tends to develop, along with practical steps you can take to mitigate it.

What Is Water Stagnation?

Stagnation occurs when water stops moving through a system. It might be sitting idle in pipework, tanks, or vessels due to low use, poor design, or outdated infrastructure. When water remains still, it loses its disinfectant protection, becomes thermally unstable, and can turn into a breeding ground for bacteria.

In large commercial systems, even minor pockets of stagnation can create compliance issues and health risks - especially if they go undetected.

Common Areas Prone to Stagnation

1. Dead Legs in Pipework

Dead legs are sections of pipework where water rarely or never flows. These often occur when plumbing systems are extended, altered, or reconfigured - but old pipework isn’t properly removed or flushed. Even if the rest of the system is in good shape, dead legs can introduce stagnant zones that promote bacterial growth. Identifying and either removing or regularly flushing these sections should be a key part of any maintenance routine.

2. Low-Use Outlets

Outlets like infrequently used taps, showers, or appliances can easily become stagnant if water doesn’t pass through them often. These aren’t always obvious - think of taps in rarely used meeting rooms, outbuildings, or maintenance areas. Implementing a simple flushing schedule, even once or twice a week, can make a big difference to water movement and hygiene.

3. Oversized Storage Tanks

If a tank is larger than it needs to be for a building’s actual demand, the water inside can sit for long periods without being turned over. This is especially common in buildings where occupancy has decreased or usage patterns have changed. Matching tank size to actual demand - and ensuring regular draw-off - helps maintain water freshness and reduces the risk of stagnation.

4. Redundant Pipework

Old or abandoned pipework left connected after system upgrades or building modifications can cause trouble. These hidden lengths of pipe may not see any flow but can still hold water, making them prime locations for stagnation and bacterial colonisation. Any legacy infrastructure that’s no longer needed should be isolated and, ideally, removed altogether.

5. Expansion Vessels

Expansion vessels are essential in closed-loop systems to handle thermal expansion, but they can also be overlooked when it comes to stagnation risk. If a vessel is oversized, underused, or isolated by a failed valve, water can sit inside for extended periods. These conditions make it difficult to manage temperature or ensure flow-through. Regular checks on vessel sizing, pressure, and operation are important in keeping them safe and functional.

Preventative Measures

Regular Flushing Protocols

A proactive flushing regime is one of the most effective ways to combat stagnation. This includes all outlets — not just those used daily — and should be tailored to the building’s layout and usage patterns. For high-risk areas, flushing may need to be logged or monitored as part of a wider compliance strategy.

System Design Optimisation

Plumbing systems that are well-designed from the outset are far less likely to suffer from stagnation issues. This means reducing the number of dead ends, avoiding over-complicated pipe layouts, and selecting pipe sizes that maintain appropriate flow rates. Reviewing older systems during refurbishments is a good opportunity to make lasting improvements.

Temperature Control

Water temperature plays a major role in bacterial activity. Hot water should be stored and circulated above 60°C, and cold water should stay below 20°C wherever possible. Monitoring systems that track these thresholds help identify problem spots before they become health hazards.

Routine Maintenance and Inspections

Stagnation often creeps in where visual access is limited - inside closed tanks, long pipe runs, or out-of-sight fixtures. Scheduled inspections of tanks, valves, vessels, and outlets help catch early warning signs. Checking for insulation failures, slow-flowing outlets, or changes in usage can reveal hidden risks before they escalate.

Key Takeaways

• Stagnation isn’t always obvious, but it can undermine even the most robust water system.

• Dead legs, low-use outlets, and oversized tanks are frequent culprits in commercial buildings.

• Regular flushing, good system design, and active temperature management are critical for control.

• Maintenance teams should treat stagnation risks as a routine part of water hygiene strategy.

Conclusion

Water stagnation doesn’t need to be a complex problem — but it does require consistent attention. For facilities managers, understanding where water is most likely to sit still, and taking steps to keep it moving, is central to maintaining a safe, efficient, and compliant building.

To learn more about stagnation in commercial water systems, why not check out our Learning Centre, which has a library of information available to help you keep your systems safe and compliant.