This diploma thesis presents reader with current knowledge in the field of gray wastewater reuse. The theoretical part describes the current state of water in the world, thus characterizes wastewater and describes its treatment. Further, this section describes the possibility of obtaining thermal energy from wastewater. At the end of the theoretical part, the reader is presented with some existing buildings in the Czech Republic that use the wastewater re-use technology system. In the following practical part, all the knowledge from the theoretical part are applied for a concrete project of construction of a graywater re-use technology system in the area of Vlněna in Brno city.