Impact of Gray Water Reuse on The Performance of Wastewater Treatment Plants in Jordan Hani Abu Qdais & Rana Halalsheh Civil Engineering Department, Jordan University of Science & Technology. Email hqdais Abstract= Gray water reuse is gaining an increased importance. Nowadays, several countries of the world are utilizing this technology on a reasonable scale. In an attempt to transfer this technology to Jordan, some pilot projects in Jordan were recently launched to investigate the feasibility of such practice. The main objective of this paper is to assess the impact of separating the gray water from wastewater stream on the wastewater treatment plants performance in Jordan.  A mass balance approach used in this study revealed that the treatment plants would be hydraulically under loaded when diverting the gray water from the treatment plants. However, the plants will be subjected to higher organic loads that may reach to triple the design value of the plants in some cases. This will affect the performance of the treatment plants and will lead to noncompliance with wastewater standards. The study concluded that it is necessary to develop national guidelines for utilization of gray water and to initially apply the gray water reuse in rural areas that are not connected to the sewer network. Further studies on pilot scale that cover the wastewater plants performance are recommended.