Analysis of profitability of rainwater harvesting, gray water recycling and drain water heat recovery systems

Abstract Gray water recycling and economical use of rainwater can be a valuable alternative source of water, especially for non-potable uses. These sources are seen as the basis of change in waters management, which gives a possibility of protection of still shrinking water resources. Taking into account continuing urbanization and population growth in the world, not only the management of water resources requires a change in attitudes, but also the management and conservation of conventional fuels that energy is generated of, and that are required for the development and functioning of urban areas. Bearing this in mind, some studies have been performed in order to establish the cost-effectiveness of application systems capable of reducing the demand for tap water and electricity used to heat it. A financial analysis with an application of the Life Cycle Cost methodology has been conducted for a multi-family residential building for seven different variants of installation of water and sewage, which assumed the use of the following solutions: gray water harvesting system, rainwater harvesting system and drain water heat recovery units. This analysis showed that the use of these systems in the tested building is financially viable, despite the fact that their implementation is associated with incurring higher investment cost than in the base case (Variant 0). The study was expanded by a sensitivity analysis on the basis of which it was possible to conclude that the project involving the use of alternative sources of pending water and energy in this building is only slightly susceptible to changes in calculation parameters.