*2.1. Description of the Study Area*

Wastewater and water resources contributing to the flow in ZR were studied. A catchment area of 4120 km2 located in the north of Jordan contributes to the natural streamflow in ZR [31]. The ZR Basin has an arid climate in the east and the southeast. In contrast, the western parts have typical Mediterranean climates that are semiarid in Amman (Capital of Jordan) and dry sub-humid in Ajloun, where rainfall exceeds 560 mm. The western parts are mountainous and characterized by cool temperatures in winter and mild temperatures in summer. The annual rainfall ranges from more than 500 mm

in the northwest to less than 100 mm in the east, with an average annual precipitation of 250 mm [32]. The basin hosts 60% of Jordan's population and 85% of all industries in Jordan, and its flood plain is used for agriculture [32]. The water downstream in ZR includes treated effluent from Assamra WWTP and surface runoff and stormwater generated during the rainy season (December–April) [33]. Assamra WWTP treats an average of 365,000 m3 day−<sup>1</sup> of municipal wastewater and industrial wastewater for the population of 2,270,000–3,300,000 PE [33,34]. The primary use of ZR water is irrigation fodder and vegetable crops in fields within the ZR flood plain [32]. This study area was also investigated in our previous study, and more details of the area can be found in Shigei et al. [35].
