We help nature along: treatment plants clean river and lake water, which then percolates into the groundwater

There is an ample supply of groundwater in Berlin and the surrounding areas due to favourable geological, hydrogeological and climatic conditions. Nevertheless, even with its abundant water resources, we cannot draw unlimited amounts of drinking water from this region without certain considerations. Our groundwater reserves need to be managed in an economically feasible and environmentally sound manner. Quantity and quality vary somewhat from catchment area to catchment area, so individual waterworks must develop different solutions for the management of groundwater resources for each respective area. They must take into careful consideration any deficit in the amount of water available and also pay close attention to any potential hazards due to industrial and natural contamination.

Sufficient amounts of groundwater do not always form naturally. Therefore, in order to be able to extract the required quantities, we at Berliner Wasserbetriebe replenish the groundwaterwith treated surface water. This is achieved by impounding water into shallow earth basins or into natural ponds and ditches. As the soil in Berlin is mostly made of sand, i.e. a waterpermeable material, water can percolate easily through it and flow down to the groundwater. The upper layers of soil act like a giant filter. The natural cleaning power of the soil improves the quality of the water physically, chemically and biologically, so that it is comparable to that of natural groundwater. On the way to the wells, percolated water also reaches the same temperature as groundwater. Apart from the Kuhlake in the Spandau Forest, all of the water bodies of the Grunewald chain of lakes area (Schlachtensee, Krumme Lanke, Grunewaldsee, Hundekehlesee and Waldsee) in particular act as natural soakaways. Earth basins have been built near the Tegel and Spandau waterworks. In and around the Stolpe waterworks, surface water from the Havel River is filtrated on the Havel meadows.

The surface water is pre-treated before it is used for filtration purposes. In two treatment plants for surface water, the substances that can be filtered out, as well as the phosphates and nitrates, are reduced using the flocculation-sedimentation-filtering principle. In this process, flocculating agents are added to the water and then filtered. The Beelitzhof surface water treatment plant purifies water from Wannsee Lake, which is then discharged into the Grunewald lakes. Prior to treatment, this water contains around 0.4 milligram of phosphorus per litre. This quantity of nutrients benefits algae growth and therefore endangers the biological equilibrium of the lakes. After the purification treatment, the water contains less than 0.01 milligram of phosphorus per litre. The water quality in Schlachtensee Lake has improved significantly and visibly as a result of this. Prior to the commissioning of the surface water treatment plant, more than 1 milligram of phosphorous was contained in one litre of water. Now, there is only around 0.03 milligram of phosphorous per litre.

Another success is the water that has been flowing into Tegeler Lake, which has been treated in the Tegel surface water treatment plant since 1985. This plant not only treats effluent which is discharged from the Schönerlinde wastewater treatment plant and carried along the Nordgraben and the Tegeler Fliess stream, but also treats water pumped through a supply pipe from the Oberhavel. This increases the water exchange rate in the lake. With depth levels of around three metres, Tegeler Lake is now one of the cleanest bodies of water in the Berlin Spree-Havel system.