Helena Sales Ortells Doctorate

Research into health risks in urban water systems

On 8 April 2015, Helena Sales Ortells received a doctorate for her research into the health risks in urban water systems. The research results show high risks of gastrointestinal diseases (from Campylobacter or Norovirus), but low risks of respiratory diseases, such as legionellosis and Q fever. KWR’s Gertjan Medema supervised the doctoral research.

Research background

Urban water systems offer recreational opportunities close to home, but they can also represent a health risk if the water is contaminated with pathogenic microorganisms. This could be the consequence, for instance, of the discharge of sewage water or contamination with animal faecal matter. Certain pathogenic microorganisms, like Legionella pneumophila, can also grow in the water systems. People can be exposed to waterborne pathogens through recreational activities, aerosols, household uses, occupational exposure, eating fruit and vegetables irrigated with contaminated water, or by accident. Helena Sales Ortells carried out her research on the health risks in urban water systems in order to support developers and authorities in the development and management of safe water systems.

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Several water systems and pathogens in a single analysis

The doctoral work involved a single analysis, using Quantitative Microbial Risk Assessment (QMRA), to determine the health risks in various water systems in Amsterdam: a river, a lake, a park pond, a sedimentation pond for captured rainwater, and a wadi. The pathogens studied were: Campylobacter, Cryptosporidium, Norovirus and Legionella pneumophila. Additionally, in sub-studies, the health risks in the following contexts were also researched: recreation in a rainwater-capture system (water plaza), irrigation of vegetables with treated sewage water containing Norovirus, and drinking water produced from groundwater during the 2009 Q fever outbreak.

High risk of gastrointestinal disease

The results showed a high risk of gastrointestinal disease (from Campylobacter or Norovirus), but low risks of respiratory disease, such as legionellosis and Q fever. At sites where human faecal matter was present in the water, the concentrations of Campylobacter were higher, which raised the risk of gastrointestinal disease. Even when the faecal concentrations were below official bathing water standards, the probability of gastrointestinal disease was still significant.


It is expected that the health risks in urban water systems in the (near) future will increase because of higher temperatures, and more frequent and heavier rain events. Sales Ortells also makes recommendations in her thesis aimed at reducing the risks – for example, the removal of cross-connections between rainwater and wastewater sewers, and additional measures regarding the use of treated wastewater. She also recommends that further research be conducted into improving the QMRA models, for example, the application of methods to determine the infectivity of pathogens in water systems.