Trihalomethanes (THMS) are chemicals that are formed when naturally occurring organic materials combine with free chlorine as disinfection byproducts. In spite of the fact that there is a peril of utilizing THMs in chlorinated drinking water, the health dangers of un-disinfected water is much greater. Therefore, this study concerned with lowering chlorine dose to amount adequate to kill waterborne pathogen with low concentration of THMs compound formation. The analysis program was conducted in Qena district at 5 fixed points comprised Salhyia plant outlet and four sites represented beginnings, middle and end of the plant network to determine the presence of chlorine disinfection by-products in treated water with respect to the disinfection process. So, chlorine dose, THMs compounds concentration, temperatures and bacteriological counts were measured a long three months. The results showed that when the chlorine dose reduced gradually to 4 mg L^-1,  formation of chloroform, bromoform, dichlorobromomethane and total THM compounds in the plant outlet decreased gradually and reached to its least concentration (6.2, 3.3,0.0, 10.9 μg L^-1 respectively) and inhibited in some cases. This reduction in THM compound formation was also directly proportional to decreasing in temperature ratios. Moreover, bacteriological analysis showed that chlorine reduction did not affect its disinfection efficiency even at the end of the network. So it is recommended to reduce the population's exposure to halogenated organic compounds in drinking water by decreasing the chlorine dose without affecting the disinfection efficiency.