Legionella in hot water tanks in Brussels: the maintenance habits that protect you

What is legionella, and why does it come up with hot water tanks?

Legionella is a lung infection caused by a bacteria, Legionella, that develops naturally in water. It occurs naturally in many water sources, but it becomes a concern when it proliferates in systems where water stagnates and the temperature stays moderate for a certain length of time. Domestic hot water tanks, whether electric, coupled to a boiler or to a heat pump, are among the appliances concerned, as are the hot water networks of larger buildings.

This isn't a risk limited to old or poorly maintained systems only: even a recent tank can, under certain conditions of use, offer an environment favourable to the bacteria. The good news is that this risk is very manageable with a few simple habits and regular maintenance, without needing to worry every time a shower runs a little lukewarm.

The conditions that favour the bacteria's development

A temperature that's too low

Legionella multiplies mainly within an intermediate temperature range, neither too cold nor too hot. A tank kept permanently at a low temperature, often to save energy, can unintentionally create conditions favourable to its proliferation. Conversely, water kept at a sufficiently high temperature in the tank strongly limits its development, which is why professionals recommend never setting the temperature too low, even for the sake of saving energy.

Stagnant water, irregular use

A tank that's rarely used, for example in a home occupied intermittently, a holiday flat, a guest room or an office closed for several weeks, encourages water stagnation. Without regular circulation, still lukewarm water provides exactly the environment in which the bacteria can settle in for the long term. This is a point that's often underestimated: it's not only the age of the system that matters, but how regularly it's used.

Limescale and sediment build-up

Limescale and sediment that accumulate at the bottom of the tank over time also play a role. These deposits create areas where water circulates poorly, where heat spreads less effectively, and where micro-organisms can settle more easily. A tank heavily affected by limescale also heats less efficiently, which can make the low-temperature problem mentioned above even worse.

The maintenance habits that limit the risk

Setting the tank's temperature correctly

Setting the temperature correctly is probably the simplest and most effective step. A tank kept at a sufficiently high temperature drastically reduces the conditions favourable to the bacteria. There's a balance to be found between comfort, health safety and energy consumption, and this is exactly what we check during a service visit: is the thermostat set appropriately, and does the tank actually reach the displayed temperature, or has the sensor drifted over time?

Letting water circulate regularly

In homes that are rarely occupied, it's advisable to run the hot water at every tap regularly, even when there's no immediate need, in order to avoid prolonged stagnation. This simple habit, which anyone living in the home can follow, usefully complements the technical maintenance of the system.

Descaling and checking the anode

Periodic descaling of the tank is one of the standard operations of a thorough service. It removes the deposits that hinder water circulation and heating. We also take the opportunity to check the condition of the anode, the component that protects the tank against corrosion: a worn anode speeds up the tank's deterioration and can, indirectly, encourage the appearance of areas favourable to bacterial growth.

Draining and cleaning

Draining the tank, particularly at the bottom where deposits build up, is one of the steps we carry out during a full service. It removes sediment and limits the dead zones where water doesn't circulate properly.

Special cases: second homes, unoccupied properties, apartment blocks

Some situations deserve particular attention. A property left unoccupied for several weeks, a second home used only on certain weekends, or the communal areas of an apartment block with shared hot water circuits, all present a higher risk of stagnation. In these cases, it's worth running a heating cycle at the right temperature when returning to the property or before a period of occupation, followed by flushing the taps before any normal use.

For apartment blocks and buildings with a larger domestic hot water network, Brussels regulations impose certain monitoring and maintenance obligations, notably through collective boiler managers. We recommend checking with Brussels Environment to find out the precise obligations that apply to your type of building, as these can vary depending on the size and use of the system.

What DPS Chauffagiste checks during a service visit

During a standard boiler or domestic hot water tank service, our technicians systematically check the elements that influence the risk of bacterial growth: thermostat setting, condition of the anode, presence of deposits at the bottom of the tank, proper functioning of the safety unit, and the overall tightness of the system. We also take the opportunity to give advice tailored to how you actually use your home, as the recommendations aren't the same for a household present every day as for a property used only occasionally.

This regular maintenance is also part of the broader legal obligations for servicing heating systems in Brussels, which cover both gas and carbon monoxide safety as well as the general condition of the appliance. A well-maintained appliance remains a safer appliance, on every level.

When to call in a professional

If you notice a significant drop in hot water temperature, a tank that takes an unusually long time to heat up, unusual noises, or if your home has been unoccupied for several weeks, it's worth having the system checked before resuming normal use. Likewise, if you're unsure about your thermostat setting or the condition of your tank, having a professional check it can quickly put your mind at ease, without having to wait for the scheduled annual service.

Conclusion

Legionella in a hot water tank isn't inevitable, nor is it a subject to approach with excessive worry. It's above all a matter of proper settings, regular use and ongoing maintenance. By building these few checks into your routine, or entrusting them to an annual professional service, you can effectively limit this risk while keeping an efficient, economical system. DPS Chauffagiste remains available to answer your questions and schedule the service of your hot water tank in Brussels.