Access to reliable, real-time water quality analysis in remote regions is essential for environmental monitoring and public health. Traditional spectrophotometric methods, while accurate, are expensive and not suitable for in situ use, especially in low-resource contexts. This research addresses the lack of affordable portable instrumentation by proposing the development of a rapid, tailored, and low-cost optical spectrometer capable of characterizing water samples directly at the collection site. The main objective of this work was to design and implement a portable optical system using accessible components and open-source technology for the optical analysis of water from rural sources in Ecuador. A descriptive and experimental methodology was followed, encompassing three phases: theoretical analysis of optical systems, simulation of optical and electronic subsystems using FreeCAD and Proteus, and the physical construction of a working prototype with 3D-printed parts and a custom PCB. The system integrates a white LED, plano-convex lenses, adiffraction grating, a 3DU33 phototransistor, and an Arduino Nano with Bluetooth transmission. Water samples from four different sources were tested and compared with a commercial spectrophotometer (DR-2010). The prototype showed good agreement in the visible range with an acceptable standard deviation, making it a viable and economical alternative for field-based water quality monitoring. Future enhancements will focus on improving calibration accuracy and optical resolution.