The Tiznit region has an arid to semi-arid climate. Rainfall is scarce and the reuse of wastewater for crop irrigation is common, and consequently groundwater can be contaminated by chemical and biological pollutants. A wastewater treatment plant is constructed with the aim of producing water suitable for reuse in agriculture and reducing groundwater pollution. The aim of this study is to assess the impact of factors that may influence groundwater quality, namely wastewater reuse and fertilizer use in the region. Groundwater was collected monthly over 1 year from five shallow wells (P1–P5) and analysed for a range of physicochemical and microbiological parameters. Concentrations frequently exceeded the WHO standards for potable water. The average concentration of nitrate was 98 mg/L. Conductivity varied from 1,930 to 2,500 µS/cm over four of the wells but was 11,703 in P3, which was close to the treatment plant. Bacteriological contamination was also found, with total coliforms varying from 0 at P1 to 9,000 cfu/100 mL at P4 and fecal coliforms (FC) 0 in P1, P2, P3 and P5 but up to 250 FC/100 mL at P4. Fecal streptococci (FS) varied from 0 to 3,500 FS/100 mL at P4. These values widely exceeded the limit for bacteria in water (0 units/100 mL).