This article presents the results of an analysis of the economic viability of using an installation for the treatment of grey water. Economic indicators in the form of simple payback time (SPBT) and net present value (NPV) were used in the analysis. The use of a dual water supply system should theoretically enable the reduction of the costs of both water supply and sewage disposal, ensuring investment profitability. The article presents the impact of the number of residents as well as the impact of water and sewage on the profitability of using example water-recovery systems. It was found that both factors have a huge impact on the result of the economic analysis. For a small number of residents and at a low price of water supply and sewage disposal, it is not profitable to invest in a water-recovery system. This is due to the high price of purification devices.