In Mongolia, as worldwide, communities are challenged by water scarcity, depletion and pollution. Greywater treatment and reuse could partially meet water demand and help protect the environment and health. In March 2010, greywater from six randomly sampled households in the Ger areas of Ulaanbaatar, Mongolia, was analyzed followed by the development of three innovative treatment systems: an underground (UG-), greenhouse (GH-) and ice-hole greywater treatment unit (IH-GWTU). The UG- and GH-GWTU were implemented to identify opportunities and challenges for future investments in greywater treatment and reuse. Users' and non-users' perceptions, and business opportunities, were assessed. Laboratory analysis showed a high chemical oxygen demand (6,072–12,144 mg/l), N-NH4+ (183.7–322.6 mg/l), PO4− (12.6–88.2 mg/l) and total suspended solids (880–3,200 mg/l) – values exceeding the WHO guidelines and much higher than in any other country: low water consumption combined with traditional diet might be major reasons. Odourless and colourless water after treatment in a UG-GWTU lead to more acceptance than a GH-GWTU. Business opportunities include the use of treated water for irrigation, considering WHO and national standards. Further research focuses on seasonality of installation, technical shortcomings, maintenance, biological quality control and user training.