Dear natural swimming pool operators,
on the occasion, we would like to update you on the current status of the Coronaviru’s situation in relation to natural swimming pools.
In addition to the Federal Environment Agency (UBA), the German Society for Natural Bathing
Wasser (DGfnB) issued a statement regarding the coronavirus situation:
In conclusion, the UBA states;
According to the current state of knowledge, the new type of coronavirus SARS-CoV-2 is transmitted primarily via the direct contact between people or contaminated areas. The likelihood of infection in the swimming pool is therefore comparable to other places in public space. Swimming and bathing pool water in Germany is treated and disinfected in accordance with the generally recognized rules of technology. For swimming pools that are built and operated in accordance with these standards, it can be assumed that the water quality is hygienically perfect and that the swimming pool water is well protected against all viruses, including corona viruses, if the water treatment corresponds to the generally recognized rules of technology and if in particular the flow, treatment and operational control are carried out in accordance with standards.
However, it must be ensured that the cleaning and disinfection measures in the swimming pool are strictly followed.
Basically, baths with biological treatment pose a higher risk of infection compared to conventionally prepared baths, which should be pointed out to the bathers on site.
According to the UBA, therefor there is protection against viruses in the pool water of outdoor pools with biological water treatment. If the evaluation of the Corona Virus leads to the fact that crowds of people are still considered dangerous during the bathing season, the gathering of many people will probably be more dangerous than bathing in biologically treated water.
The DGfnB writes:
There is also no evidence that the virus would survive in the water at all, and if so, for how long. However, it is much more likely that other bathers could be infected already on the way to or in the pool.
It remains to be seen how the experts from the Robert Koch Institute will further assess the situation.
In order to support you – as an operator – in the meantime to better understand natural pools in relation to viruses, there are a few brief explanations and tips for measures below.
Viruses and bacteria in natural pools are broken down within the pool water by zooplankton (1), competitive pressure from other organisms, possibly allelopathic mechanisms (release of growth-inhibiting substances) and UV radiation (IOB 2013). Outside the basin, it is broken down using external filter systems (2).
The mechanisms mentioned, which lead to the breakdown of viruses and bacteria in the pool water, can only be influenced with difficulty in the short term by the operator. In the long term, however, the establishment / replanting of planting zones in the pool edge areas / on the wet filter surfaces will help. This creates growth and protection areas for zooplankton and creates a higher level of biodiversity, which leads to the support of ecological competitive pressure and the promotion of allelopathic mechanisms.
The breakdown of viruses and bacteria through filters can be effectively increased by increasing the circulation rates, since germs are eliminated during each filter passage. The Federal Ministry for the Environment demands that the filter parameters in natural outdoor pools be reduced by one log level (90%) after a filter passage (E. coli, enterococci, Pseudomonas aeruginosa) (UBA 2003). The indicator parameters are bacteria. The latest virus-related study comes from the University of Alberta, Canada. In the model investigations, mean degradation performance of a Neptune filter of 1.35 log levels was measured with respect to noroviruses. In a combination filter consisting of a hydro-botany and a wet filter, the dismantling performance was even included
2.35 log levels (Petterson 2019). The degradation performance of noroviruses was therefore significantly higher than the degradation performance of the indicator parameters of one log level required by the Federal Environment Agency. If one considers the fact that coronaviruses are approx. 4 times larger than noroviruses and are therefore probably easier to be retained in the filter, it is shown that if they can survive unexpectedly in the water, they are very likely to be broken down . A current risk assessment for noroviruses showed that a pelvic circulation rate of two revolutions per day should be maintained in order to keep possible noroviruses within the tolerable range (Bruns 2020). As a preventative measure, this value could also be related to corona viruses.
The mechanisms mentioned, which lead to the breakdown of viruses and bacteria in pool water, can only be influenced with difficulty by the operator in the short term. In the long term, however, the establishment / replanting of planting zones in the pool edge areas / on the wet filter surfaces helps. This creates growth and protection areas for zooplankton and creates a higher level of biodiversity, which leads to the support of ecological competitive pressure and the promotion of allelopathic mechanisms.
- The virus elimination by the zooplankton essentially depends on the species present (different zooplankton have different filtration capacities) and the amount present. The quantity, in turn, depends on the ecological conditions (available food supply, ecological environment of the bath, presence of planting zones as retreat areas, etc.). It is assumed that the zooplankton filter by filtration on average 4% of the pool water per day and thereby eliminate viruses and bacteria (FLL 2011). Depending on the ecological conditions, the filtration capacity can also exceed 80% of the pool water / day.
- Whilst the elimination performance of the zooplankton can sometimes be lower depending on the ecological situation, the soil filters are significantly higher and more constant in the degradation performance. Elimination services of 90-99.9% are assumed here (IOB 2013, BRUNS / PEPPLER 2019).
ls is well protected against all viruses, including the corona viruses, according to the current state of knowledge, the following measures can be taken to improve the degradation performance:
- Expansion and intensification of the planting in the corresponding areas (hydro-robotics and wet filters)
- Check the current circulation capacity / day and if necessary increase the filter capacity to two pool circulations / day
If you need support with the measures, please feel free to contact us. We wish you all the best and best health.
Greetings, Hannes Kurzreuther
Polyplan-Kreikenbaum Gruppe GmbH
Ingenieure und Architekten für Technische Gebäudeausrüstungöffentliche Bäder, Landschaftsarchitektur und Umwelttechnik
Bruns S./Peppler C. (2019) Hygienic quality of public natural swimming pools (NSP), IWA Publishing, S.
UBA (2003) Empfehlung des Umweltbundesamtes – hygienische Anforderungen an Kleinbadeteiche (künstliche Schwimm- und Badeteichanlagen), Bundesgesundheitsblatt – Gesundheitsforschung – Ge- sundheitsschutz
Bruns S. (2020) Naturfreibad Borden Park in Edmonton (Kanada) – Projektvorstellung und Risikobewer- tung, Veröffentlichung voraussichtlich: Archiv des Badewesens, Mai 2020
FLL (2011) Richtlinien für Planung, Bau, Instandhaltung und Betrieb von Freibädern mit biologischer Wasseraufbereitung (Schwimm- und Badeteiche), Forschungsgesellschaft Landschaftsentwicklung Land- schaftsbau e.V. (FLL), Bonn
IOB (2013) Performance of Public Swimming Ponds -An Overview of Hygiene in Pools with Biological Wa- ter Purification, Internationale Organisation für naturnahe Badegewässer (IOB), Bremen
Petterson S. (2019) Assessing the enteric pathogen risk within Natural Swimming Pools – case Study: Borden Park, Edmonton, Canada, University of Alberta, School of Public Health, Presentation at the 10th international IOB Congress
UBA (2020) Stellungnahme des Umweltbundesamtes Coronavirus SARS-CoV-2 und Besuch in Schwimm- oder Badebecken beziehungsweise Schwimm- oder Badeteichen, Umweltbundesamt, Bad Elster