This book addresses the design and implementation of a Programmable Logic Controller (PLC) based on open technology for the control and automation of a water treatment system. It starts with the Arduino development environment as a base, seeking to convert this solution into a more robust and accessible one for industrial environments. Chapter 1 details the proposal, scope and objectives, based on the requirements of the treatment plant, and introduces open technology tools. Chapter 2 describes the design development, from the selection of the microcontroller and electronic components to the printed circuit board design and 3D modeling of the housings. The control logic and programming code are discussed. Chapter 3 presents a comprehensive cost analysis, including component, manufacturing and programming costs, to evaluate the economic investment. Finally, Chapter 4 synthesizes the findings and results, evaluating the fulfillment of the objectives and pointing out limitations and areas of improvement for future developments.