C*t is used as a metric for disinfection in a water treatment plant while inside a distribution system, the concentration alone is used. For systems without a treatment plant, however, chlorine may be added in the upstream portion of the system to disinfect water. Therefore, disinfection is increased at higher chlorine concentration levels but also with enough contact time to completely disinfect the water. Therefore the use of the C*t product as a metric in the distribution system, if no upstream treatment exists, is explored here through computer modeling. The network solver EPANET was used to simulate the C*t product using water age in a method introduced here. It was found in a demonstration project that increasing the mainline pipe diameter allows the water to slow down enough to allow the C*t product to fully disinfect the water prior to reaching the first users. Specifically, for the demonstration system analyzed, an 8-inch (203 mm) mainline diameter requires 1.0 mg/L of chorine addition at the upstream end to fully disinfect the water. This shows promise for the use of pipe enlargement as a disinfection method for systems with no water treatment plant.