Our scientific research is based on oxidation reactions and monitoring of chemical reaction kinetics in the Velekinca groundwaters plant in Gjilan municipality, Kosovo. The GW of this plant contains high concentration of manganese so we need to use potassium permanganate (KMnO4) as one of the most power oxidants in the water treatment plant. In our research the high concentration of Mn in groundwaters is 0.22–0.28 mg∙dm–3 and this concentration is not in accordance with the WHO. Chlorine is one of the most common disinfectants used in the water treatment industry because it has a low cost and immediate effect on the destruction of microorganisms, the concentration of chlorine (Cl2) in our research is 0.1–0.32 mg∙dm–3. The speed of chemical reactions in the technology of GW is extremely important because sometimes in the elimination of chemical pollutants using oxidizing agents often form intermediate species. The speed of reactions indicates how fast chemical bonds are formed in the creation of a product, and this depends on the rate of reaction (XA). The focus for the research is to study the potassium permanganate and chlorine gas reactions in water if it forms intermediate products (intermediate species) due to the high speed of reactions. Scientific research conclusion, intermediate species in the oxidation reactions of Mn and water disinfection with Cl2(g) it is impossible to cause a high rate of chemical reactions from the reaction rate (XA = 1%) to the reaction rate (XA = 99%). The maximum speed at the highest XA Cl2 is from 4.405∙10–11 to 8.87∙10–10 mol∙dm–3∙s–1, while at Mn is (2.030–4.034)∙10–7 mol∙dm–3∙s–1.