Kuala Langat Power Plant (KLPP) draws water from the Kuala Langat River. The quality of river water varies significantly from season to season due to the influence of rainfall and surface water runoff. The turbidity of river water varies in the range of 70-500 NTU with lower value typically noted in the summer and higher value during the rainy season. Conventional chemicals such as Alum & Lime were used for pretreatment of water. As per Malaysian Environmental laws alum sludge is categorized as scheduled waste. Hence, an alternative environment friendly & biodegradable Poly diallyl dimethylammonium chloride (DADMAC) studied for pre-treatment of water. Laboratory test and plant trial were conducted using poly DADMAC as coagulant for pretreatment of water. It is observed that 2.0 ppm of poly DADMAC is effective for removal of turbidity up to 300 NTU and higher concentration. Zeta potential was observed to be in the range of -1.8 to -3.7 ICU indicates strong agglomeration & precipitation tendency. The treatment does not alter pH & conductivity of treated water and treatment cost is in agreement with Alum & Lime treatment.