A story of water treatment

Felix: Where are we going for holiday this year?

Donau Chemie Water Technology
Papa, where are we going for holiday this year?
Hm, good question. Have you seen anything you might like?

There are so many beautiful places. Lake Garda! We've already been there. Look, there's a funny picture: people riding their bikes across the water.
This is Isola di San Biago on the south-west side of the lake. This island is actually only accessible by boat. By the way, it is also called Isola dei Conigli, the Rabbit Island.

Are there any rabbits?
In the past, yes, but now they are certainly hiding themselves in the face of the many tourists.

And why can people now walk on water like Jesus?
Due to the low rainfall in recent years, the water level of Lake Garda is lower than it has been for a long time. The low water level creates a land bridge between the island and the mainland. Oddly, this already happened in February. The inflows into the lake were significantly lower, so that the level of the lake was already about 50 to 60 cm below the average water level in winter.

50 cm - that's not so much, is it?
As you may remember, Lake Garda is quite large. 50 cm less water means that the lake is missing 200 billion litres of water. That could supply all the inhabitants of Austria with water for half a year.

Oh! That's really a lot of water. Is it still possible to swim in it at all?
Yes, of course - after all, the lake is over 100 m deep on average and over 300 m deep at its deepest point. But it is an important water resource for the northern Italian region, for drinking water production, for industry and of course for agriculture. For Italy's largest river...

I know it! That's the river Po!
Exactly, the water of Lake Garda is an important tributary for the river Po. However, the island of San Biago is only a symptom of a much larger problem that affects not only Italy, but large parts of Europe and also other regions of the world: there is a lack of abundant rainfall, the river levels are correspondingly low, the soils are drying out. Already last summer, ships on the Rhine could sometimes hardly operate, power plants all over Europe could not work at full capacity, people were urged to save water. Austria is also affected. Last year, the Zicksee dried up completely. If it then rains heavily, the water cannot percolate sufficiently, runs off quickly and entire areas are flooded extremely fast. This is exactly what happened recently in Italy.

I know - the poor fish first lack water and then suddenly have too much.
The climatologists note that the total amount of precipitation in Austria has not changed significantly in recent years. However, heavy rainfall events have become more frequent and evaporation has increased significantly. As a result, the water runs off quickly, the groundwater level remains low and the soils dry out. Droughts have always existed, but recently they have occurred more frequently and will happen at increasingly shorter intervals in the future.

That doesn't sound good at all...
That is true. The time has come to find solutions to the problems. In many countries, for example, water losses must first be addressed. In some EU countries, 20 to 30 percent of drinking water is lost through leaking pipes. In Italy, Romania and Malta it is 40 percent and in Bulgaria even 60 percent. Imagine buying ten bottles of water at the supermarket and coming home with only four full bottles.

Then I must have been very thirsty on the road....
We also need to manage our water resources better. In many regions of the world, the reuse of wastewater will be a possible solution.

For drinking? Ugh!
Primarily for the irrigation of agricultural land. The European Union has just drafted a regulation on minimum requirements for the reuse of water, which will come into force at the end of June. It sets out the quality requirements that must be met in the agricultural reuse of wastewater. The main issues are coliform bacteria and the total organic load of the water. The quality must be monitored and risk management is mandatory. This can result in further precautionary measures such as additional disinfection steps or elimination of trace substances in the sense of a multi-barrier system.

I know the answer to that - you can do it with activated carbon or with your Donau PAC Aquaclear.
Brilliant thinking. That's right! And we also have disinfectants, of course. In any case, the standards for the water will increase. Our coagulants will also play an important role. Because the better the sludge can be separated from the water in the sewage treatment plant, the lower the residual load. It is well-known that precipitation and flocculation can also reduce the bacterial count by up to two, sometimes even three log levels (99.9 %). This relieves the burden on all subsequent treatment steps. For comparison: washing hands removes approx. 99% of germs (i.e. 2 log levels).

Is this being done in Europe at all yet?
According to the EU, about 2.4% of wastewater in Europe is reused. The estimated potential is at least six times higher. Cyprus already uses 90% of treated wastewater for irrigation, Greece, Italy and Spain between 5 and 12%. But there are also projects in countries like Belgium and Germany.

How is the situation in Austria?
Currently, 1.7% of agricultural land in Austria is irrigated. Around 69 billion litres of water are consumed annually for this purpose.

That's less than Lake Garda is missing now!
That is correct. However, the demand for irrigation in Austria could increase by 80 % until 2050, and regionally - especially in the east and south of Austria - even an eightfold increase is imaginable. Here, the reuse of wastewater could reduce the pressure on groundwater resources. However, it must be taken into account that in the affected rural regions the amount of wastewater is lower and thus the effect is limited. Nevertheless, even a small relief is an important contribution.

Will recycled wastewater also come out of our water pipes at the end of the day?
Probably not in Austria. In other regions of the world this has been implemented already for a long time, e.g. in Singapore or Namibia. While in Singapore a water reservoir serves as a buffer between the sewage treatment plant and drinking water production, in Windhoek (Namibia) the sewage treatment plant effluent can also be fed directly into the multi-barrier drinking water production system, especially in drought periods. The high requirements, the constant monitoring and the lack of alternatives have led to a high level of acceptance among the affected population. For us, this may still be difficult to imagine. But experiences in Namibia show that it is safe. Because cases of disease caused by polluted water have not occurred there since then - it works.

I'm sure the Namibians will be happy about that. I hope mankind can solve the water problem soon. It's working, as you said. Then there will again be more water in Lake Garda and the rabbits on the island will have their privacy again. And I can sit on the shore and eat delicious Italian ice cream.


  • Bichler, D. A., & Müller-Rechberger, D. H. (2023). Rahmenbedingungen für die Umsetzung der EU-WasserWVVO in Österreich. Wiederverwendung von gereinigtem Abwasser. Wien: ÖWAV / TU Wien, Institut für Wassergüte und Ressourcenmanagement.
  • Dipartimento della Protezione Civile. Situazione lago di Garda. Abgerufen am 13.. April 2023 von Enti Regolatori dei Grandi Laghi: https://www.laghi.net/homepage.aspx?tab=3&subtab=2&idlago=5
  • Europäische Kommission. Water reuse. Abgerufen am 17.. April 2023 von https://ec.europa.eu/environment/water/reuse.htm
  • Haslinger, K. (2023). Auswirkungen des globalen Klimawandels auf Österreich. Wiederverwendung von gereinigtem Abwasser. Wien: ÖWAV / TU Wien, Institut für Wassergüte und Ressourcenmanagement.
  • LAHNSTEINER, D. D. (2023). Direct Potable Reuse in Namibia – Erfahrungen aus Anlagenbau- und Betriebsführungssicht. Wiederverwendung von gereinigtem Abwasser. Wien: ÖWAV / TU Wien, Institut für Wassergüte und Ressourcenmanagement.
Donau Chemie Water Technology


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