The aim of this study was to evaluate trends in water quality and mineral footprint along the catchment of a dam located in a coal mining area and water-stressed region. The study was conducted along the upper Olifants River, which is the catchment of Witbank Dam, in the jurisdiction of Emalahleni Local Municipality in South Africa. The study analysed water quality data over an eight-year period, obtained from the water authorities, and two-year data from the municipality. The analysis focused on water quality determinants such as pH, turbidity, total dissolved solids, sulphates and manganese. The analysis was conducted in line with South African National Standard 241:2015 on drinking water. By using allowable mineral concentration limits and thresholds, a statistical process capability index was calculated to determine the efficiency of controls on the potential of water being contaminated by land use and mining activities. It was found that the coal mining region was associated with adverse effects on the raw water quality. The paper presents a generic method in terms of a concentration-independent process capability index for monitoring deterioration of water across many water quality determinants. The results provide a warning signal to stakeholders. There is a time-critical and growing deterioration of water quality, which may pose health risks to consumers if there is no reduction in contamination sources or improved efficacy of water purification systems.