This study focuses on the performance evaluation of a large cylindrical CeBr₃ detector (76 mm × 76 mm) for detecting nickel concentration in contaminated water samples. Using prompt gamma neutron activation analysis, water samples contaminated with different concentrations of nickel (2.7, 5.0, and 6.5 wt.%) were investigated. By analyzing gamma rays emitted at 8993 and 9498 keV, originating from nickel, the net nickel counts were derived by comparing the sample spectrum with the background spectrum. These net counts exhibited a proportional relationship with the concentration of nickel in water. Additionally, it was assumed that the cohesive yield of the peak with nickel in the difference spectrum of each sample corresponds to its respective nickel concentration. By employing linear regression analysis, a robust correlation (R² = 0.997) was established between the cohesive yield of the net peak related to nickel and the corresponding nickel concentration in the analyzed water samples. The minimum detectable concentration (MDC) was determined by calculating the two peaks entire counts. It was determined that this MDC was 0.0815±0.0250 wt.%, or 815±250 ppm. These results demonstrate the remarkable evaluation of the CeBr₃ detector in accurately identifying the presence of nickel in water samples, as evidenced by its ability to detect even very low concentrations based on the total counts of the two peaks.