In the present study, the concept of ‘Sample alteration of surface water’ has been employed to improve the efficiency of the aluminum-based electrocoagulation (EC) treatment method for the removal of reactive fractions of natural organic matter (NOM) from chlorinated water. The characteristics of surface water have been slightly modified by adding mine water in different ratios. The process has been optimized using the response surface methodology (RSM) considering pH, current density, mix ratio, and contact time as factors. At the optimized condition, the EC method has significantly reduced total organic carbon, dissolved organic carbon (DOC), and UV254 absorbance values up to 24%, 27%, and 80%, respectively. The cumulative impact of sample alteration and EC method has exhibited outstanding coagulant activity in terms of UV254 abs, DOC, turbidity, phenol, and absorbance slope index (ASI) as well. A decrease in ASI values indicated the reduction of trihalomethane's formation in water-containing chlorine. This was validated by reduced chlorine demand. It can be concluded that mixing mine water with surface water can be a feasible and efficient method for treating water with a high NOM content.