The Rimac river watershed is characterized by its over exploitation of natural resources, such as mining activities and hydroelectric power, this fact makes necessary to assess water quality on its main affluent rivers. In this work, we apply the center-point triangular whitenization weight functions (CTWF) method, which is based on the grey systems theory that is an approach from artificial intelligence. In the case study, we analyze the following Rimac river affluents: Blanco river, Aruri river, Rimac river, Mayo river, and Santa river. The monitoring data on each affluent were obtained from Water National Authority of Peru (ANA). The CTWF method was applied using parameters of water quality such as O2, DBO, DQO, SS, NH3, and NO3. Then, the results were ranked using the Prati scale. Consequently, the results showed that all affluents classified as uncontaminated within the Prati scale, which means that these should be treated by conventional methods to be purified. However, the affluent Blanco river was more vulnerable to be contaminated. Finally, the results of this study could be used by local authorities or central government to make the best decision on the Rimac river watershed management.