In Germany, ensuring water supply is a mandatory duty of the state. Responsibility lies with the municipalities, which can use a range of organisational and legal forms to comply with this duty. Applied to the abstracted water volumes this means that the public water supply abstracted around 5,1 billion cubic meters of water to supply the population with drinking water. Groundwater reserves are the most important source of drinking water. In Germany, ensuring water supply is a mandatory duty of the state. Responsibility lies with the municipalities, which can use a range of organisational and legal forms to comply with this duty. A total of 10 billion cubic meters of waste water was treated in public sewage plants in 2010, almost exclusively through biological waste water treatment.