Legionella Control in Complex Water Installations Without Extra Chemicals

In the Netherlands and Belgium, hundreds of cases of legionellosis are reported annually, with likely underreporting as not every case of pneumonia is tested for legionella. For building managers, swimming pool operators, and technical services, this isn’t just an abstract number but a daily responsibility: providing safe water, even when installations are large, branched, and partly stagnant.

This article zooms in on legionella prevention in complex water installations, especially on the question of how to reduce risks without having to keep dosing extra substances. We look at the role of biofilm as a refuge, why temperature and flushing are not always enough, and how targeted ultrasonic applications can fit into a modern control plan as an additional measure.

Why complex installations often present 'surprises'

In a compact residential installation, hydraulic behavior is usually predictable. In hotels, care facilities, sports complexes, ships, and industrial sites, things are different. There, you encounter:

• long pipe runs and infrequently used tapping points
• buffer vessels, storage and day tanks
• variable occupancy (seasons, peak times, vacancies)
• mixing valves and temperature zones where lukewarm water can stagnate
• dead legs after renovations or function changes

It is precisely this combination that makes legionella control without chemicals attractive for organizations wanting to limit their environmental impact, but it also makes designing measures more demanding. A plan that only says 'keep temperatures high and flush weekly' quickly hits its limits in practice.

Biofilm as a Safe Haven: What Happens in Pipes and Tanks

Anyone wanting to control legionella cannot ignore biofilm. In many installations, the vast majority of microorganisms are not free-floating in the water, but attached to the inner walls. This slimy matrix acts as a protective layer and breeding ground, where bacteria can nest and reseed.

With biofilm and legionella in water tanks, you often see the same pattern: even if the bulk water (the water you sample) seems temporarily 'good,' underlying adhesion in tanks, shower pipes, or flexible hoses can remain the source. Moreover, biofilm is rarely homogeneous; it forms patches, especially in areas with:

• low flow rates
• rough surfaces, limescale deposits, or corrosion
• variable temperatures, for example around mixing zones
• sedimentation at the bottom of tanks

Managing biofilm in drinking water installations, therefore, is not just cleaning 'when there is a problem,' but a structural strategy to reduce adhesion and dismantle existing layers.

Why Temperature Management and Flushing Routines Aren't Always Sufficient

Temperature remains an important pillar. But in complex networks, it's difficult to consistently achieve the desired values everywhere and to prove this is always the case. Flushing helps to reduce stagnation, but it doesn't guarantee that adhesion disappears. There are also practical limitations:

• Flushing requires water and labor, especially in buildings with many tapping points.
• Stagnation still returns during vacancies or nighttime operation.
• Some pipes are 'flushed' without achieving the right flow rate or duration.
• Biofilm can quickly regrow after flushing if the adhered layer remains intact.

That's why many managers look for additional legionella measures alongside flushing routines, preferably measures that work continuously, require little maintenance, and fit within sustainable management.

Pools, Wellness, and Showers: Extra Focus on Aerosol Formation

In wellness environments, the responsibility is even more prominent: showers, misters, and bubble areas create fine water droplets that can be inhaled. Legionella safety in pools and wellness facilities is thus not just about water quality, but also about exposure routes.

The challenge is twofold:

1. there are often many tapping points and wet areas with varying usage
2. installations sometimes combine drinking water components (showers) with process water-like sections (buffers, technical circuits)

Therefore, a control plan should clearly demarcate: where drinking water logic applies, where process water logic applies, and what monitoring is associated with each.

Standards and Supervision: What’s Coming in 2026?

Norms and regulations for legionella prevention focus on risk management, demonstrability, and periodic control. In 2026, the emphasis in practice will increasingly be on:

• keeping the risk analysis up-to-date during renovations and function changes
• demonstrable execution of control measures (logbooks, sensor data, records)
• quick follow-up of deviations, including reassessment of root causes
• attention for installation parts that are 'forgotten': dead pipes, emergency supplies, seasonal sections

For buildings and maritime environments, this means a legionella risk analysis for buildings and ships should ideally not be written once, but be periodically adjusted based on use, incidents, measurements, and technical changes.

Ultrasound as an Additional Measure: Targeting Adhesion, Not Dosing

Where chemical methods often work via concentration in the water, ultrasound focuses on mechanical energy: vibrations that disrupt adhesion conditions and can help dismantle existing layers. This makes it interesting as an environmentally friendly legionella prevention technology, especially in settings where the addition of substances should be limited.

Nuance is important: ultrasound is not a replacement for a management plan, but it can be a reinforcing link. Think of:

• tanks where sediment and wall adhesion keep recurring
• long pipe sections with structurally low flow
• installations where chemical load or byproducts should be minimized
• situations where you want to maintain continuous 'pressure' on biofilm formation, even outside of flushing moments

In practical terms, ultrasonic legionella control in pipes is about integration: where to position transducers, how to ensure operational reliability, and how to combine this with temperature, flushing, and monitoring.

How Ultrasound Fits Into a Control Plan Without Ignoring the Basics

Integrating ultrasound into a legionella management plan works best when you have a sharp goal upfront. A few realistic goals:

• reducing adhesion in high-risk sections (tanks, branches, hot water circuits)
• slowing recolonization after cleaning
• lowering the 'baseline load' of biofilm in the installation

At the same time, the following remains true: good hydraulic design, avoiding dead legs, correct temperatures, and discipline in execution are the foundation. Ultrasound is an extra layer in the measures package.

Note: every installation is different. Therefore, always have an assessment done to see if an additional technique suits your risks, materials, flow rates, and operations, and record choices in your documentation.

Practical Approach for Facility and Technical Teams

Legionella prevention for technical services and facility managers works best with an approach that is both technically and organizationally sound. These steps help move from 'firefighting' to structural management.

1. Update the risk analysis based on usage, not just the schedule
   Consider occupancy rates, seasonal closures, renovations, new tapping points, and temporary bypasses.
2. Make biofilm visible in your thinking and inspections
   Not everything can be detected with water samples. Consider inspections of tanks, filters, shower heads, flexible hoses, and critical mixing zones.
3. Evaluate the effectiveness of flushing
   Are time, temperature, and flow rate being achieved? Is there evidence in logging or measurements?
4. Choose additional measures where the problem originates
   If biofilm keeps returning particularly in a tank or pipe section, focus measures there. This can range from cleaning regimes to continuously operating support.
5. Ensure follow-up and accountability
   Make execution easy: checklists, digital records, clear escalation in case of deviations.

Where NDV Ultrasonic.com is Often Involved in Practice

At NDV Ultrasonic.com, requests often come from environments wanting to be less dependent on dosing and wanting to address biofilm structurally. With years of experience in high-frequency ultrasonic technology, in industries such as manufacturing, shipping, and recreational water environments, we often contribute to the logic behind the application: where does adhesion occur, which parts of the system determine the risk, and how do you make a management plan robust without unnecessary environmental impact.

Those wanting to delve deeper into adhesion and why that layer is so persistent, can start with the explanation on the biofilm page. For practical experiences from various sectors, the references often provide recognition, especially for teams struggling with recurring contamination in tanks and pipes.

In Conclusion: Adding Fewer Substances Starts With Smarter System Thinking

Anyone wanting to keep legionella under control in large, branched systems cannot rely on just one lever. Temperature and flushing remain valuable, but in complex installations, risk management calls for extra layers: insights into stagnation, focus on biofilm, and technology that continuously helps to limit adhesion. This is exactly where legionella control without extra chemicals comes into play as a strategy, not just a slogan.

Would you like to discuss your installation, for example for a building with multiple risers, a wellness environment, or an onboard drinking water network? Then check where NDV Ultrasonic is active via where we can help or contact us directly via the contact page.