Healthy water, healthy people: how we build knowledge for a safer future

Shifting patterns driven by climate effects

Eline Boelee is one of the researchers who studies the links between water, ecology and public health on a daily basis. She coordinates the Water, Soil and Health expertise area at Deltares and works on BlueAdapt and One Health PACT, among other projects. BlueAdapt is a European project that examines how coastal water quality is changing as the climate warms, and what this means for swimmers, food chains and water managers. Within the project, Deltares develops new knowledge and models to identify and limit health risks at an earlier stage. One Health PACT focused on insect-borne infectious diseases.

Boelee notes that the public health impacts of climate change are becoming more visible. Research within One Health PACT revealed the complexity of these changes. "We now have West Nile virus in the Netherlands," she explains. "The virus is brought by birds from other regions. As the climate warms, migration routes are shifting, and we see more infected birds carrying the virus here."

At the same time, the common house mosquito, which can transmit the virus, thrives in slightly brackish water. Salinisation and land subsidence — both exacerbated by climate change — are creating more places where this mosquito can reproduce, particularly in coastal areas. "Natural enemies, such as dragonflies and amphibians, struggle in brackish water. This gives the mosquito more space, increases its numbers and allows infectious diseases to spread more quickly," Boelee adds. The risks extend beyond mosquitoes.

Rising temperatures also favour pathogens in surface water. "We see Vibrio bacteria flourishing alongside algal blooms," says Boelee. "They often occur together with phytoplankton, which develops more strongly in warmer conditions. Vibrio bacteria can cause infections in swimmers through direct contact, and in people who eat contaminated shellfish.

Health impacts of warming and extreme rainfall

Within BlueAdapt, Deltares focuses primarily on how climate change influences the spread of pathogens in coastal areas. Two Dutch case studies are central: Katwijk and Lake Grevelingen.

In Lake Grevelingen, researchers study how Vibrio bacteria respond to rising temperatures, algal blooms, and changing nutrient conditions. They analyse which Vibrio bacteria are present, whether there are interactions between plankton and bacteria, and the roles of temperature and sediments. These findings are linked to climate scenarios to predict potential health risks for swimmers and shellfish farms.

The work in Katwijk focuses on sewer overflows triggered by heavy rainfall. "Sudden peak rainfall accelerates runoff, overloading sewers and increasing the likelihood of overflows," says Boelee. This leads to temporary spikes in coastal pollution. While measures such as rainwater disconnection and local water retention help reduce the frequency and impact of overflows, extreme rainfall remains a challenge. Katwijk uses the purple warning flag to inform beach visitors of short-term reductions in water quality. "At the same time, warmer weather brings more recreational activity — exactly when the water can be less safe for swimmers."

To help, Deltares is developing a predictive model that indicates when bacterial levels rise in the sea near Katwijk. The focus is on E. coli, a key bacterial indicator of faecal contamination. "We model how this bacterium behaves under the influence of UV light, temperature and currents," Boelee explains. "That allows water managers to run what-if scenarios and plan ahead."

The value of predictive water management

"At many bathing locations, water quality samples are taken only once every two weeks," Boelee notes. "Results typically become available two to three days later, so water management is always behind the curve." As a result, beaches may remain closed unnecessarily, or stay open too long when risks are higher. Mussel and oyster farmers can also face needless harvest restrictions.

With these new models, Deltares aims to shift the system from reactive to predictive water management. Over time, this should lead to real‑time warning systems for swimmers, farmers, and water managers.

Microplastics as carriers of health risks

Beyond climate change, plastic pollution is an urgent health concern. Micro- and nanoplastics end up in water, soil, air and food, and now also in the human body. Microbiologist Dr. Anniek de Jong works at Deltares on the MOMENTUM and TULIP projects, which investigate how plastic particles move through water systems and the microbial risks associated with them.

"Plastics act as transporters," De Jong explains. "Once plastic particles enter water, a biofilm forms; bacteria attach and multiply. That makes it easier for pathogens and antibiotic-resistant bacteria to spread." This is sometimes called the 'Trojan horse' effect: microplastics acting as carriers of hidden risks.

A second mechanism is the exchange of genetic material between bacteria. "Within biofilms, bacteria appear to exchange DNA more rapidly," says De Jong. "That includes genes that confer resistance against antibiotics." This accelerates the spread of antibiotic resistance genes in water systems.

Bacteria and antimicrobial hotspots in focus

MOMENTUM examines the potential health risks of microplastics and explores ways to prevent these. Partners range from hospitals to universities and research institutes. In this project, Deltares focuses on how environmental conditions influence the development and composition of microbial communities on microplastics, with particular attention to potential pathogens and antibiotic resistance.

The team combines fieldwork with laboratory experiments. "Partners produced different types of plastic. Some were exposed in the field at wastewater treatment plants, rivers and agricultural ditches; others were incubated under controlled laboratory conditions," De Jong explains. After exposure, the plastic particles were collected and analysed to determine which microorganisms had colonized them, including pathogens and antibiotic resistance genes.

"In additional experiments, we examined the influence of metals and other chemicals that can stress bacteria," says De Jong. "We found that higher concentrations of these substances are associated with increased levels of antibiotic resistance genes." Such stress conditions may trigger bacteria to activate or amplify resistance mechanisms.

The TULIP project investigates how plastic particles transport antibiotic resistant bacteria in river. Partners in Europe and the Philippines collect field data, which Deltares integrates into models to identify key transport pathways and hotspots of antimicrobial resistance. Although the health risks in the Netherlands are relatively low, sources such as hospital effluent and agricultural runoff do contribute to the spread of antimicrobial resistance.

"Internationally, the risks are higher," De Jong notes. In some tropical regions, more plastic particles and higher antibiotic concentrations accumulate in water bodies. . These conditions create strong selection pressure: susceptible bacteria are suppressed, while resistant variants, including those living in biofilms on microplastics, gain a competitive advantage. "As a result, resistant bacteria can spread more rapidly, especially in regions where people depend on river water for daily activities."

MOMENTUM results

Deltares’ work within MOMENTUM comprised two consecutive phases. MOMENTUM 1 focused on building fundamental knowledge about micro- and nanoplastics and identifying potential health risks. MOMENTUM 2.0 built on that foundation, deepening the research to better understand and analyse those risks.

Read more about the results of MOMENTUM 1; the results of MOMENTUM 2.0 will be published on this page shortly. You can also consult the Microplastics and Health knowledge agenda, which outlines current evidence, outstanding questions and future actions.

A broader view of healthy water and soil systems

BlueAdapt, MOMENTUM and TULIP all align with the overarching Deltares mission: strengthening healthy water and soil systems. Boelee describes such systems as those that can absorb change while remaining healthy for nature and people. "Ultimately, healthy water and a healthy planet are fundamental to human health," she says.

This broad approach requires close collaboration within and beyond Deltares. "We connect source control, the environment and health," De Jong explains. Knowledge is continuously shared across projects, with close cooperation among partners in the Netherlands and internationally. While Deltares focuses on research and modelling, other partners ensure that insights reach policymakers, for example in Brussels, allowing new guidelines and measures to better align with practice.

By linking science, collaboration and policy, the research achieves greater social impact. It leads to more reliable models, more effective measures and a stronger approach to cross-border challenges such as antibiotic resistance, plastic pollution and climate-sensitive pathogens.

Embedding health in future‑proof water management

The need for predictive tools will continue to grow. Step by step, models are being developed that indicate when bacteria levels are increasing or where health risks may emerge. De Jong hopes that health will become a integral part of water management, in the Netherlands and beyond: "So that negative effects are prevented and positive effects amplified."

Meanwhile, research is moving fast. Within TULIP, measurements are under way in Rome and the Philippines. Plastic particles are released into rivers and later analysed to understand how pathogens and resistant bacteria develop on plastics surfaces. These field data will be combined to refine computer models of dispersion and biofilm formation.

The follow‑up to MOMENTUM focuses on other routes of plastic exposure and therefore lies outside Deltares’ water‑related expertise. Initial results from BlueAdapt have been shared with European policymakers. One goal remains central throughout: improving and protecting public health.