Drinking water becomes waste water after use. Before this used water can be returned to nature, it must be safely drained from the houses and cleaned.
Berlin’s drinking water comes from groundwater resources under the city. It has[SO1] formed over more than 10,000 years under deep layers of stone, earth and sand.
The groundwater replenishes itself again and again with precipitations and surface water. It passes through several layers of solid and in doing so is treated in a natural way and acquires valuable minerals. This is why groundwater is so suitable as a resource for drinking water abstraction.
In some areas in which the groundwater cannot replenish itself sufficiently, we supply it with pretreated water from rivers and lakes. To this end, it is impounded in shallow earth bank basins or in ponds and ditches.
Around 650 deep wells with 30 to 140 metre depth pump the groundwater to the waterworks. Here it is treated to produce drinking water. Our vertical filter wells can pump 40 to 400 cubic metres of water an hour to the surface. Our three horizontal filter wells achieve up to 1,600 cubic metres per hour.
Berlin has established several water protection areas to keep the water in the area around our wells clean.
We carry the groundwater from the wells to one of our nine waterworks. Here we treat it and store it in clean water tanks. Berlin’s households, industry and commerce require an average of around 546,000 cubic metres of fresh drinking water – every day. This is the equivalent of almost 400 filled 50 metre swimming pools. We are able to provide up to 1.1 million cubic metres per day – almost twice as much.
Berlin’s water supply is monitored and controlled by an instrumentation and control system from three control rooms in Friedrichshagen, Tegel and Beelitzhof. The waterworks coordinate the central control. In this way we can ensure a high delivery capacity and supply all households.
Our water and intermediate pumping stations are connected by a 7,816 kilometre long pipe network. Around 275,000 building connections or service pipes lead from the supply pipes, or local mains, to your tap. In addition, 69,300 hydrants and 93,000 isolating valves ensure that the drinking water supply functions smoothly. We control the pressure and flow at numerous points in the pipe network so that even high buildings can be supplied.
Drinking water becomes wastewater. Thanks to gravity, it flows through building connection sewers, so-called laterals or service connections, to the main sewer in the roads and from there through ever larger sewers to pumping stations, which pump it to the wastewater treatment plant. We always keep an eye on the path taken by the wastewater.
Berlin is divided into drainage areas. The wastewater sewers always lead to the lowest point in a drainage area. A pumping station is located there, which pumps the wastewater through pressure pipes to the wastewater treatment plant.
Berlin’s wastewater sewers are 9,746 kilometres long. This is roughly the distance from Berlin to Lima, the capital of Peru. Three quarters of the areas of Berlin connected to the sewer system have separate wastewater sewers for foul wastewater and rainwater. One quarter of the city – mainly the area within the urban railway (“S-Bahn”) ring – is drained in a so-called combined system, in which rainwater and foul wastewater are carried in the same sewers.
Berlin’s wastewater treatment has high requirements. To meet these with know-how and technical equipment, we operate 164 pumping stations, more than one thousand kilometres of pressure pipes and six wastewater treatment plants.
In dry weather our wastewater treatment plants treat around 624,000 cubic metres of wastewater daily. This is where the different types of wastewater meet:
Wastewater can be contaminated with undissolved and dissolved materials. Undissolved materials float or sink in water. They can therefore be filtered out mechanically. Dissolved materials can only be separated from the water by biological or chemical means. In Berlin’s wastewater treatment plants the wastewater passes through all these stages one after the other.
In the mechanical treatment stage screens, a grit chamber and settlement tanks remove the coarsest dirt. In the biological treatment stage there are consecutive anaerobic, anoxic and aerobic zones. They remove phosphorous and nitrogen compounds. 97 percent of undissolved and biologically degradable, dissolved pollutants are retained in this way. The wastewater is therefore as good as clean.
In the coming years we will be equipping our wastewater treatment plants with further treatment stages such as flocculation-filtration and ozonisation to further improve this treatment capacity. These stages further reduce phosphorous and nitrogen compounds and protect bodies of water. In the Schönerlinde wastewater treatment plant a modern plant is also being built to remove trace substances.
Once the wastewater has been treated we discharge it into rivers and lakes. From there it infiltrates through the rock and into the groundwater over a long period of time. The cycle starts all over again.
In Berlin, an average 590 litres of precipitation per square metre and year falls as rain, snow or hail. By way of comparison: If all that fell on one day, the whole of Berlin would be knee-high under water.
Because the city is growing and becoming more compact, more and more areas are being made impervious by being surfaced. Many green areas and brownfield sites are lost as a result. This is not only bad for wildlife and the cityscape: The city also needs unsurfaced, pervious areas for the retention, evaporation and percolation of surface water.
The impervious surfacing interrupts the natural water balance. The water increasingly flows away on the surface. The result: In the summer Berlin becomes a heat island, and plants and trees dry out. And the problems are getting worse. Climate change will probably cause more hot periods or heavy rainfall than to date.
Our sewer system is designed for “normal” rainfall. In the event of more infrequent heavy rainfall events, it quickly reaches its capacity limits and runs full. Roads and tunnels are flooded and combined wastewater flows into the bodies of water.
Unfortunately, we cannot simply increase the size of the sewers everywhere. The space underground is limited and such projects are expensive. Moreover, the sewers would then be over-dimensioned and too large for “normal operation”. The wastewater would no flow away as well and odours and rust would occur. Therefore, the surface water has to be handled differently in case of infrequent heavy rainfall events: It must evaporate, percolate or be stored.
In future the State of Berlin will try new solutions instead of only relying on discharge into the sewers. The objective for new build projects and existing built land is: decentralised or local management and support of the natural water balance. We call it the “sponge city Berlin”.