Engineers involved in designing, implementing and operating water purification processes face great challenges when implementing purification plants with the lowest construction cost and greatest operating efficiency considering the aim of obtaining the best water quality. This article investigated the optimal designing steps for a drinking water purification plant on the Orontes River in Homs, Syria. The demand for water was evaluated and the design steps for the units and calculations were presented, after a statistical analysis of the measurements of the quality and quantity of water at different times was performed. Some parameters related to the physical and chemical characteristics were outside the permissible limits, depending on the water quality a conventional treatment processes were suggested. These designing steps can be adopted by any designer when designing a plant on a water source compatible with the studied water.