In this study, we describe a sustainable system for treatment and reuse of grey wastewater in urban areas through vertical green walls constructed on unused surfaces of buildings. The system integrates the benefits linked to the introduction of green spaces in urban areas with the advantages connected with the reuse of purified greywater (non-potable reuse) and the reduction of potable water use, allowing a sustainable use of water resources. We constructed a vertical green wall composed of modular panels with 12 vegetated pots per panel. The green wall was irrigated with synthetic greywater, and the removal efficiency was monitored weekly with regards to different parameters (e.g., BOD5, COD, nitrogen, phosphorus). The results showed good results in terms of treatment performances, indicating the suitability of the green wall for treatment of greywater.