Decision makers in the wastewater industry face demographic changes in terms of a decreasing population and a declining quantity of wastewater. This results in technical hurdles and economic challenges. The economic challenges are caused by the durable and capital intensive infrastructure that can only be adapted in a very limited extent to the changing environment. The fixed costs add up to 75-85% of the total costs and they have to be covered by a reduced number of feepayers, causing an increase of the wastewater fees per capita. This article analyses three case studies for the following questions: How strong a wastewater company is affected by demographic change? How will their wastewater fees increase due to demographic change? The article analyses beside the decreasing number of inhabitants (demographic effect), the impacts of decreasing water demand of the households (water saving effect) and of the industry (industry effect) as well as the development of the future operational expenditures (opex effect) and of the capital expenditures (capex effect) in order to compare the different effects and to identify the decisive fee drivers.