In mid-March 2025 Waterleau announced that its staff would join the Watermonsters campaign – the largest citizen‐science effort ever conducted on Belgian waterways. As we noted on LinkedIN, Waterleau volunteers “put on their boots to investigate the E. coli contamination in the surface water”.

Together with 5,000 other citizen scientists in Flanders and Brussels, Waterleau employees collected water samples as part of the Watermonsters project, organized by Waterland vzw, De Standaard and KU Leuven. Waterleau emphasized that supporting this initiative aligns with its mission to protect water as a resource. By serving as an official sponsor, Waterleau both funded the campaign and mobilized its workforce to map local water quality.

Watermonsters was formally launched on 15 March 2025 by Waterland vzw (a Flemish water advocacy group), the national newspaper De Standaard and scientists at Belgium’s largest university KU Leuven. The goal was to engage 5,000 citizens as “water monsters” to test the health of streams, canals and rivers across Flanders and Brussels.

Organizers provided each volunteer with a simple test kit (to be used between 25 April and 4 May) and an interactive map. The campaign focused on detecting Escherichia coli, a bacterium that indicates untreated sewage. As the organizers explain, E. coli normally lives in human intestines, so high concentrations in water imply recent wastewater discharges. By empowering citizens to measure E. coli in their local waters, Watermonsters aimed to fill data gaps and “reclaim the waterways” for safe use. In practice the survey covered all flowing waters from the rural countryside to urban canals – “from the Flemish countryside to the centre of Brussels” – ensuring both rural and urban watercourses were sampled.

The campaign’s objectives were twofold: to map the current state of water quality in Flanders and Brussels, and to raise public awareness of pollution issues. By comparing E. coli levels against EU bathing-water standards, the project would show which sites are safe for recreation. Public officials were also urged to use the results to improve wastewater management. In his June 2025 press release, Waterland’s Lieven Symons noted that the project “encourages people […] to claim the right to clean rivers,” highlighting that open waterways should be safe for swimming, boating or fishing.

The Watermonsters project was a joint effort by civic organizations, media and academia. Waterland vzw (a water policy think-tank) coordinated the field campaign; Newspaper De Standaard provided publicity, the interactive map platform and data collection; and KU Leuven led the scientific analysis of samples. Other supporters included Aquafin (the Flemish sewage company), the environmental NGO Natuurpunt, Bond Beter Leefmilieu (the Flemish green league) and the National Lottery. In media coverage these groups emphasized that Watermonsters is the “largest citizen science project ever” on Belgian water quality. Funding came from sponsors like Waterleau, Aquafin and the lottery, with labs at KU Leuven handling the E. coli tests.

Waterleau played a key role as sponsor and participant. On World Water Day (22 March 2025) Waterleau publicly announced its backing on LinkedIn. Waterleau underscored that Watermonsters’ goal – to “identify pollution sources and push for real change” – aligns with the company’s mission of sustainable water management.

In practice, Waterleau encouraged its own staff to sign up as “citizen scientists.” Over the registration period (March 15–30, 2025), employees joined with volunteers nationwide. In late April we received kits and sampled nearby waters during the designated week. For example, teams tested local streams (e.g. the Kleine Nete near Wespelaar) and canals. The Waterleau volunteers followed the standard protocol and submitted E. coli test results back to KULeuven.

The Watermonsters results were published in the weekend of 7 June 2025. In total volunteers collected about 6,000 samples across Flanders and Brussels. After quality checks, roughly 5,700 measurements remained for analysis. Each sample was classified by E. coli level into ‘good’, ‘acceptable’ or ‘poor’ quality. The key findings were striking:

• About 43% of tested sites had E. coli levels below the EU threshold, making them safe for bathing.
• Conversely, roughly 42% of sites exceeded the standard due to high E. coli contamination. These poor-quality sites are unsafe for swimming.
• There was a clear contrast between large and small waterways. In the major rivers and canals, pollution is diluted by high flow: about 86% of those samples met the safety standard. In other words, almost all samples from big navigable waterways were clean enough for swimming.
• By comparison, smaller streams and urban canals fared much worse. As media reports noted, “our large watercourses are cleaner than expected, our small brooks and canals dirtier than expected”. Many local tributaries – often near towns or subject to sewer overflows – showed elevated E. coli.

These figures confirm that untreated household wastewater is a widespread source of contamination. In fact, the study emphasized that the measured E. coli stems mostly from homes, not agriculture or industry. Excessive E. coli indicates leaks or discharges from sewers and septic systems. In plain terms, the Watermonsters data reveal how many waterways are still burdened by raw sewage. Importantly, the survey provides hard data to target improvements: by mapping each site, it highlights hotspots and can guide where to upgrade treatment or sewer networks.

Check the full results in the interactive map here

High Connection does not imply Full Treatment Coverage

• Around 94% of households in Flanders are connected to a sewer system.
• However, not all these connections lead to actual treatment. Approximately 88–89% of wastewater is fully treated with proper purification.

That leaves over 10% of wastewater — from connected households — either untreated or only partially treated before entering water bodies.

According to KU Leuven, this non‑treated minority has an outsized effect: “12 percent of the households causes that more than half of the sampling points show poor water quality (42 percent poor, 15 percent acceptable)"

So even though treatment coverage is above 88%, those remaining untreated discharges drive most of the contamination identified by Watermonsters — particularly in small streams and canals, where there's little dilution.

Why Results Still Show High Pollution

• Household Coverage vs Effective Treatment
  • 94 % connected, but only 88–89% treated. The rest may bypass or inadequately use treatment infrastructure.
• Big Impact from Small Percentage
  • Only ~12% of households contribute untreated wastewater, yet they are responsible for over half of the sites with elevated E. coli.
• Dilution Doesn’t Help Small Waterways
  • In larger rivers, pollution is diluted (about 86% are safe), but small local streams get heavily affected by even minor discharges.

Yes — the treatment gap is around 10–12%, but these untreated discharges are precisely why many sites failed Watermonsters E. coli thresholds. Most pollution stems from household sewage, not from agriculture or industry. Until that remaining percentile of wastewater is properly treated, small watercourses will continue to show poor water quality.

Waterleau’s sponsorship of Watermonsters 2025 underscores the company’s commitment to sustainable water use and pollution prevention. The campaign results – showing widespread sewage contamination – highlight exactly the kinds of challenges Waterleau’s solutions are designed to address (e.g. advanced wastewater treatment, water reuse and nutrient recovery).

By supporting citizen science, Waterleau not only helped generate valuable data, but also elevated public dialogue on water quality. As the company’s own announcement emphasized, “every drop counts.”

Waterleau will continue to leverage these insights in its work with municipalities and industries, advocating for stronger water policies and investment in treatment infrastructure. In summary, Waterleau’s participation in Watermonsters reflects its dual role as a technical leader and as a steward of water resources, fully aligned with its mission of reducing the environmental footprint of water use.