First SURF, then SWIM

Hardly a metropolis in the world has as many natural bathing waters to offer as Berlin. A website provides information about the water quality of the bathing areas.

Website informs about the water quality of 39 Berlin bathing sites

The Havel, Spree and Dahme widen in many places to areas as large as the Wannsee, the Großer Müggelsee or the Grunewald Lakes. In some places, though, the rivers are so narrow that you can even swim to the opposite bank easily. This dammed up chain of rivers and lakes is a Berlin speciality. The water quality is good – usually. During heavy rainfall, however, pathogens can get into the water and then trigger gastrointestinal infections in bathers. Now, anyone and everyone can obtain information about health risks like this from the new web application before jumping into the water.

River bathing areas in the city centre

“River bathing areas in the city centre in particular can be a problem in extreme weather events such as heavy rain , ” explains Dr. Pascale Rouault, Head of the Urban Systems Division at Kompetenzzentrum Wasser Berlin (KWB). Here, rainwater flows through the sewage system into the waste water treatment plant along with domestic waste water. “But if it rains very heavily, this may overburden the capacity of the sewage system and the waste water treatment plant. So that streets and cellars do not flood, everything flows through combined sewer overflows into the waterways. “In rainy years this can happen up to 30 times; in particularly dry years like 2018 only a few times. It is true that river water purifies itself by natural processes. “But that may take a few days under certain circumstances. In the meantime, dirty mixed water may flow into rivers and lakes.” Specifically at the bathing areas near the city on the northern Unterhavel there is then a risk of catching an infection while swimming. The southern bathing areas of the Unterhavel, on the other hand, are less likely to be affected by microbiological pollution from the city area; here, dilution, currents, wind or solar radiation eliminate the risk.

“Flussbad Cup” in the Kupfergraben, banch of River Spree in central Berlin

The State Office of Public Health and Social Affairs (LAGeSo) tests the water quality regularly – in most places every 14 days, and in especially sensitive areas of the Unterhavel weekly. Then it takes another two days until the results are available. “The LAGeSo can therefore only warn the population if the danger has perhaps already passed,” says Rouault. This gap is being closed by the bathing water quality forecasting system developed by KWB in the context of the nationwide FLUSSHYGIENE project, which complements the regular measurements of the State Office. The Spree-Havel system in Berlin was one of four reference areas in the three-year research project funded by the Federal Ministry of Education and Research (BMBF). The forecasting tool has been in use since July 2018 at the two bathing areas Kleine Badewiese and Grunewaldturm on the northern Unterhavel. “It is a statistical model that is fed with data which is already collected daily in any case,” reports Rouault. Berliner Wasserbetriebe supplies the rainy weather data, the Senate Department for the Environment the information about how much water is flowing in the Unterhavel per second.” We bring this data together and create an added value.” The data is automatically imported, prepared and used by KWB to generate forecasts for the respective day for both bathing areas. The forecasting tool was calibrated on the basis of extensive long-term recordings by LAGeSo. “A comparison with special tests shortly after rain has shown that our computer calculations are very accurate,” emphasises Rouault. The LAGeSo is still responsible for the information regarding the water quality. “This is also useful because our early warning system provides information about short-term contamination, but the LAGeSo has longer-term information about possible blue-green algae infestation, for example, and thus can assess all the safety risks.”

Automatic sampler for microbial control of the prediction model on River Havel in Berlin

Already mote than 50,000 hits

Anyone and everyone can benefit directly from the research results and obtain up-to-date information about the water quality of the 39 official swimming areas in Berlin via the new web application. Coloured markings indicate whether or not the water is suitable for bathing on the respective day. In addition, the site provides more information about the respective bathing area, such as whether it has disabled access, whether there are toilets, parking facilities, or a restaurant. “In July and August 2018, we had almost 50,000 visits to the site, most of them from smartphones.” KWB, LAGeSo, Berliner Wasserbetriebe (BWB) and the Technologiestiftung Berlin (TSB) jointly developed the web application, which is optimised for smartphones. The fact that people can always obtain up–to-date online and mobile information about where they can swim without health concerns is in line with Berlin’s self-image as a smart, liveable metropolis, said Berlin Health Senator Dilek Kolat at the launch of the site. The Technologiestiftung also relied on publicly available data for its implementation. “It demonstrated at the same time how useful the Berlin Open Data strategy is,” says Rouault. Berlin committed itself in the E-Government Act of 2016 to making certain data accessible and more usable. Open data is intended to create more transparency and enable new business models at the same time.

Validation of prediction model by microbial analyes; River Havel in Berlin during rainy summer 2017

The new early warning system also complements the EU Bathing Water Directive. This Directive does formulate minimum requirements for the quality of bathing water and stipulates that the population must be warned in case of temporary contamination, but it does not give any limits for daily assessments. The water quality in general is only classified once a year on the basis of data from the previous four years. “Our daily forecasts could clarify the directive,” says Rouault. KWB has already been able to present its approach both in the Federal and State Bathing Water Working Group as well to experts from the EU Commission who are engaged in the potential revision of the Bathing Water Directive.

The Federal Environment Agency (UBA) is also interested. As a scientific authority, it deals with infection risks in bathing waters and has supported KWB in the development of the early warning system. “The new forecasting model is a significant gain, especially from the consumer’s point of view, ” says Camilla Beulker , Head of the Department for Drinking and Bathing Water Hygiene at UBA. Especially in urban areas with highly frequented bathing areas, it makes an important contribution to preventive health protection.