Small scale water system planning with the possible interaction of groundwater and surface water sources was undertaken for the Dow-Lie Industrial Park, Taiwan. R. O. C.. A conceptual model of general conjunctive use of groundwater and surface water system for an industrial park was initially considered. Depending on the availability of data. the conceptual model was scaled down to a working model suitable for the study area. The working model was formulated in mathematical terms as a Linear Programming Model with the objective of minimizing the annual cost of operation and maintenance of water supply scheme. The decision variables of this model were the optimal quantities of surface water and groundwater to be used for supplying the study area every month. The results suggest that surface water must be utilized to the maximum possible extent and only the deficit between the monthly demand and the quantity of water supplied from surface sources should be supplied from groundwater.