This article addresses how and to what extent a governance mode can legitimately provide public services. A single case study of the partially privatized Berlin Waterworks is used to analyse the level of input and output legitimacy as well as potential trade-offs between the criteria emerging in a public-private partnership (PPP) in the water supply and sanitation sectors. While the Berlin Waterworks as a PPP leads to a lower level of resource protection and public acceptance, it leads to a higher level of efficiency and profitability than under the previous public model.