Water scarcity is causing major concerns throughout the world, especially in arid regions where cities are growing rapidly and are depleting groundwater reserves faster than they can be recharged. The southwestern U.S., Arizona and Nevada in particular, are experiencing the large growth rates with limited water resources and no new sources available. In effort to reduce the amount of water being consumed by people, new engineering technologies are being explored. Water reuse is becoming recognized as the last untapped water resource. However, little research has been conducted on effectively distributing that water to user. In particular, distribution of reclaimed water through a parallel pipe networks system to homes or dual water supply system has not been considered. Existing distribution systems deliver water via a single system. Meeting flow and pressure requirements for fire conditions are driving factors in designing water distribution systems. Minimum regulatory pipe diameters of six to eight inches are common in most systems and can lead to reduced water quality. The goal of a parallel system is to maximize the usage of reclaimed water. By distributing non-potable water through a separate line to meet non-sanitary uses (i.e., outdoor, fireflow, and toilet flushing), the need for potable water can be greatly reduced. Separating these demands from the potable system can reduce the potable system pipe sizes, improve water quality and reduce the overall cost of the water distribution system. Some cities in the southwestern U.S. have already implemented this new system in some residential areas through a non-potable "purple pipe" system. However, the efficiency of these new systems has not been thoroughly examined. This paper will focuses on the design of dual systems by using an optimization algorithm linked to EPANET (USEPA, 2000) via the EPANET toolkit to determine the optimal least-cost design of dual piping systems.