The diploma thesis deals with the analysis of complaints from drinking water customers, particullary about water quality. Within the theoretical part, it presents both the view of the customer of the drinking water and the view of the operator of the water supply system. It also presents possible ways to use drinking water customers complaints as indicators of water system service quality. Further, the thesis focuses on the satisfaction of customers and their trust in the operators of water supply systems. An analysis of complaints of drinking water users on the quality of water that has been received by the operator during the last five years has been performed as part of the case study in the practical part of the thesis. The cases are interpreted in context of the conditions at the given site of the water supply network.