Abstract: To address the inefficiencies in information integration and operational management caused by complex processes and interdisciplinary coordination in traditional water treatment plant construction projects, a management platform for water plant buildings has been developed based on BIM and WebGIS technologies. This platform supports the entire lifecycle of water plant buildings, including design, construction, and operation and maintenance, and incorporates five core modules: model interaction, progress management, equipment management, documentation management, and user permissions. The platform achieved breakthroughs in two key technologies: semantic information lightweighting and geometric model lightweighting. First, by optimizing the IFC file parsing process and the BIM model semantic information storage structure, data writing time was drastically reduced from 13800 seconds to just 4 seconds, while storage space usage was reduced to approximately one-seventh of the original. Second, using a geometric instance mapping matrix, lightweight model visualization was implemented on the front-end, significantly improving model loading speed and interactive experience in web browsers. This study was validated through application in an actual water treatment plant project. During the construction phase, the platform effectively assists in validating the rationality of plans and enables real-time monitoring of project progress. In the operation and maintenance phase, it supports real-time monitoring of equipment operational status. Application results indicate that the platform is expected to shorten the overall construction period by 8%-12% and reduce routine equipment inspection staffing from three people per day to one, saving approximately 66% in labor costs, thereby providing a practical reference for the digital management of similar projects.