Unpleasant odours from floor drains are one of the most common and persistent issues reported in commercial buildings. Whether it is a washroom, plant room or rarely used shower area, the problem often seems to return no matter how many times it is addressed.

For facilities managers, this can become a frustrating cycle of reactive fixes, complaints and unnecessary maintenance costs. The reality is that most drain odour issues stem from a small number of underlying causes. Understanding these is the key to solving the problem properly.

How floor drains are supposed to work

Most floor drains rely on a simple but effective principle: the water trap.

A typical drain includes a U-shaped section of pipe that holds a small amount of water. This water seal acts as a barrier, preventing sewer gases from travelling back up through the drain and into the building.

When functioning correctly, this system is:

• Passive with no moving parts
• Low cost to install
• Effective at blocking odours and gases

However, it also has a fundamental weakness. It depends entirely on that water seal being present at all times.

The real reason drains start to smell

In most cases, odours are not caused by blockages or poor cleaning. They occur because the water seal in the trap has failed.

Once that seal is gone, there is nothing preventing:

• Sewer gases entering the building
• Odours spreading into occupied spaces
• Bacteria and airborne contaminants moving upwards

The question then becomes why the seal fails so often.

The most common causes of trap failure

1. Evaporation in low-use areas

This is by far the most common issue.

In areas where drains are used infrequently, such as spare washrooms, plant rooms, seasonal buildings or vacant office space, the water in the trap gradually evaporates. Once it is gone, the barrier disappears completely.

This has become more prevalent with hybrid working patterns, where parts of buildings may sit unused for extended periods.

2. Siphonage and pressure changes

Drainage systems are not always static. Changes in pressure within the pipework, often caused by large volumes of water moving elsewhere in the system, can pull water out of traps.

This can happen during peak usage periods, in poorly vented systems or in multi-storey buildings with shared drainage stacks.

The result is the same. The trap is emptied and the seal is broken.

3. Capillary action and wicking

Materials such as hair, debris or fibres can sit across the trap and gradually draw water out through capillary action.

Over time, this slowly reduces the water level until the seal fails.

4. Cracks, leaks or poor installation

In some cases, the issue is structural. Cracked pipework, poorly fitted traps or incorrect gradients can all lead to water loss.

Even small leaks can allow the water seal to drain away, particularly in older buildings or areas with heavy usage.

Why traditional fixes do not solve the problem

A common short-term fix is to pour water into the drain to restore the seal. While this can temporarily eliminate odours, it does not address the root cause.

In practice:

• The water will evaporate again
• Pressure changes may remove it again
• Maintenance teams must repeat the process regularly

Other approaches, such as chemical treatments, may mask odours but do not prevent sewer gases or pests from entering the building.

This creates an ongoing maintenance burden and increases the likelihood of issues being missed between inspections.

A different approach to sealing drains

The core issue with traditional systems is reliance on water to create a seal. In real-world buildings, that is difficult to maintain consistently.

This is where solutions such as Green Drain offer a more robust alternative.

Green Drain works in a completely different way to a traditional water trap. Instead of relying on standing water, it uses a flexible one-way silicone membrane.

• Water can pass through the membrane freely
• Sewer gases cannot travel back up through the drain
• Insects and pests are physically blocked from entering

Because there is no reliance on a water seal, the system cannot dry out. This removes the single biggest cause of drain odours.

Why Green Drain is a better solution to recurring odour problems

For facilities managers dealing with repeated drain issues, Green Drain addresses the underlying weaknesses of traditional traps.

It eliminates the risk of evaporation

Since Green Drain does not rely on water, it continues to function even in low-use areas such as plant rooms, vacant spaces or seasonal buildings.

It reduces maintenance requirements

There is no need to regularly top up traps or apply chemical treatments. This reduces both labour time and ongoing maintenance costs.

It improves hygiene and compliance

By physically blocking sewer gases and pests, Green Drain helps maintain a more hygienic environment and reduces the risk of complaints or audit issues.

It is quick and easy to install

Green Drain can be installed in seconds into existing drain outlets, making it a practical retrofit solution without disruption.

It supports sustainability goals

By removing the need for chemical treatments and reducing water usage associated with maintaining traps, it offers a more environmentally responsible approach.

Moving from reactive fixes to long-term prevention

Drain odours are rarely random. In most cases, they are the predictable result of a system that depends on conditions that are difficult to maintain in day-to-day building operation.

By understanding how and why traps fail, facilities managers can take a more proactive approach. This includes identifying high-risk drains, incorporating checks into PPM schedules and considering alternatives to water-based seals.

In many cases, introducing a simple physical barrier such as Green Drain can resolve the issue at source, rather than repeatedly treating the symptoms.

A more reliable long-term approach

For facilities managers under pressure to reduce maintenance workload, improve hygiene and control costs, drain performance is often overlooked.

Yet it is an area where small changes can have a significant impact.

Replacing or supplementing traditional traps with a solution like Green Drain provides a more reliable, low-maintenance way to prevent odours, block pests and maintain building standards over time.