Most utilities use some forms of chlorine to safeguard drinking water from bacteria re-growth and biofilm formation during water supply transportation and distribution. It could increase the threats of disinfection by-products (DBPs) formation –mainly trihalomethanes (THMs)- in water. In this paper, a mathematical model that expresses THMs concentration in terms of initial chlorine dose, total organic carbon, bromide ion concentration, contact time, temperature, algae, and pH is developed from experimental bench studies. Another objective of this paper is to characterize the main aspects of water quality deterioration in a distribution system. The effect of residence time on chlorine uptake and the formation and evolution of disinfection by–products in distributed drinking water are discussed.