The investments made by German local communities and network operators in the removal of wastewater, which amounted to €15.5 billion in the period from 2002 to 2004 [1, 2], were predominantly allotted to the public sewerage area, with a share of €11.4 billion, i.e. 73.5 %, while the remaining share of 26.5 %, or almost € 4.1 billion, was allotted to public wastewater treatment. High fixed costs are characteristic of water management: around 75 to 85 % of the total costs arise irrespective of the amount of wastewater. 49 % is allotted just to the imputed interest and the depreciation of buildings and structures [3], whose service life can vary within a broad bandwidth in accordance with the LAWA guidelines on the carrying out of cost comparison calculations [4]. Today, service lives are sometimes calculated that are significantly longer than is covered by the guidelines. This procedure is only sensible and responsible, however, if the calculated service lives can actually also be achieved.
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