The N.E.R.D. Watermaker Controller is an open-design embedded system developed for the control and monitoring of marine reverse osmosis watermakers. Built around the ESP32 platform, it provides a reliable and flexible interface to manage pumps, flushing cycles and system parameters, while continuously monitoring pressure, flow and water quality (TDS). This manual describes the functionality, structure and philosophy of the controller, offering a clear reference for installation, configuration and operation. Designed for real-world use, N.E.R.D. gives full control to the operator without enforcing rigid automation logic, making it suitable for custom and DIY watermaker systems. Open by design. Built for real-world use.