The photocatalytic degradation of cresol red was studied using ZnO as semiconductor. Sunlight was used as the source of energy. ZnO is an extensively used photocatalyst because of its chemical stability, nontoxicity, and low cost. Parameters like pH, BOD, COD, DO, conductivity, TDS, alkalinity, hardness, calcium, magnesium, chloride, fluoride, sulphate, nitrate and turbidity were observed in present experiments. It was observed that photocatalytic degradation mainly affects the parameters like COD, BOD, nitrate, sulphate and hardness. Increased BOD, conductivity, decreased COD, pH, hardness, alkalinity and significant release of SO4 2− confirm the mineralization of the polluted water during this treatment process.