For fear of legionella in Zurich
Schools use 127,500 liters of water during the holidays
In the city of Zurich, schools have to turn on all the taps once a week during the summer holidays. This creates a lot of unused wastewater – it’s not wasted, because: This prevents legionella.
Published: 07/02/2022 at 17:01
Chiara Schlenz and Sven Ziegler
In the summer holidays, the corridors in the schools remain empty. The classrooms are deserted – and the numerous water taps in the schools in the city of Zurich remain closed. At least six days a week.
Once a week the water in all classrooms has to be made to flow. The water must run for at least one minute, the education authorities require. The reason: fear of legionella. The rod-shaped bacteria can cause flu-like illnesses and severe pneumonia.
According to the Federal Food Safety and Veterinary Office (BLV), infections with Legionella occur again and again in Switzerland. In 2019, the Sentinella reporting system of the Federal Office of Public Health (BAG) recorded 582 cases of legionellosis, five to ten percent of which were fatal.
127,500 liters of water are used for prevention
But there is no reason to panic: “Legionella are always found in small quantities in drinking water, but they can exceed the legal maximum if the water is still in the pipes for a long time at temperatures between 25 and 50 degrees,” says Daniel Bekcic, specialist communication at Immobilien Stadt Zürich zu Blick. Legionella feel extremely comfortable in these temperatures – and multiply accordingly quickly.
The recommendation to let the water run during the summer holidays comes from the BAG and the BLV and is considered a “recognized rule of technology” in the industry.
Bekcic cannot say exactly how many rooms there are in the schools in the city of Zurich and how many faucets the school caretakers have to turn on and off every week. However, more than 1700 classes go to school in the 116 school buildings in the city area. As each of these classes requires a room and these rooms also have running water & thousands of faucets are opened and run for a minute each week.
On average, around 15 liters of water flows through an average tap every minute. This means that hundreds of liters of water flow unused from the tap directly into the sewage system every week. A quick calculation reveals a remarkable figure: the measure uses around 25,500 liters of water per day – extrapolated to 127,500 liters of drinking water during a five-week summer vacation. For comparison: a person uses an average of around 129 liters of water per day.
Costs for sanitation higher than for drinking water
However, Bekcic does not want to know anything about wasting water. “At first glance, this may seem wasteful, but it is absolutely necessary,” he says. It’s a risk assessment. Should there actually be a legionella outbreak as a result of the water standstill, the availability of the systems would be restricted for a certain period of time. In addition, the costs for remedial measures would be significantly higher than the “costs for operational prevention” – for example the water drained off.
The measure is also not new, but is based on the ordinance of the Federal Department of Home Affairs (EDI) on drinking water and water in publicly accessible bathrooms and shower facilities, explains Bekcic. However, Immobilien Stadt Zürich has only been actively drawing attention to the measure for two years.