Current Research Trends and Challenges Related to the Use of Greywater in Buildings

This paper presents a review of current trends and challenges in greywater use in buildings, with particular emphasis on toilet = flushing applications. It discusses the quantitative and qualitative characteristics of greywater, including its generation sources, share in total domestic wastewater volume (50–89%), and flow variability depending on residents, building type, and user habits. Implementation of greywater recycling technologies faces several challenges, such as parameter variability, stringent sanitary and epidemiological standards, and the presence of micropollutants, including pharmaceuticals. Technological barriers include the integration of multi-stage treatment systems (physical, biological, and chemical) and ensuring effective disinfection for indoor use. The paper also highlights the lack of uniform international regulations and the significant variation in recovered water quality requirements. Key physicochemical and microbiological indicators that determine treatment system requirements are presented, with particular emphasis on the removal of organic pollutants and indicator bacteria. Various physical, chemical, and biological treatment technologies are described, with hybrid systems offering high efficiency and user safety. The implementation of greywater recycling systems encounters technical, regulatory, and social barriers. Social acceptance and transparent monitoring are identified as key challenges for widespread adoption. This critical literature review summarises current knowledge on effective greywater management in buildings, representing an increasingly important issue for sustainable water resource management.