The urban water management must address new challenges. Examples include the impact of demographic trends and climate changes or the implementation of resource protection measures. New Alternative Sanitation Systems (NASS) represent one potential approach, where technologies are used to close as far as possible the water and material cycles for the purpose of recycling the valuable components present in wastewater. The planning and implementation of NASS principles are described in the Standard DWA-A 272. An integral part of NASS according to Standard DWA-A 272 is the treatment and reuse of greywater. Following numerous research projects and long-term scientific studies, greywater reuse systems produced industrially for the treatment of separated greywater flows within the building services engineering are available on the market. However, to date there exist no technical regulations for these systems. The Guideline DWA-M 277 can be applied to systems which process and supply service water from greywater for private as well as public/commercial buildings, or which treat the greywater and discharge it. These include, inter alia, single- and two-family houses, multi-family houses and large residential complexes, administrative and training institutions. Moreover, this document can also be applied to systems in the commercial sector such as in hotels, guest houses, sports facilities, camping sites and restaurants. The present Guideline provides information and assistance for the planning, design, construction, operation and maintenance of greywater treatment and reuse systems for different applications. Systems, which do not treat the generated greywater, are not covered by this document. This Guideline is the result of cooperation between the Association for Rainwater Harvesting and Water Utilisation - Darmstadt (fbr), the Training and Demonstration Centre for Decentralised Wastewater Treatment - Leipzig (BDZ) and the German Association for Water, Wastewater and Waste - Hennef (DWA). The aim of cooperation is to establish and regulate the technical basis for the installation and operation of greywater reuse systems according to their application as separated flow treatment within NASS in the building services engineering, and to introduce it to the professional public.