This study presents a comprehensive sustainable water quality improvement model and an indicator evaluation model specifically applied to the artificial lake at the Guangzhou Foreign Language School Campus. Situated adjacent to an active construction site, the lake’s deteriorating water quality posed significant risks to both the local ecosystem and the health of students and staff. The results show that we observed a significant improvement in water quality over a treatment period of approximately 730 days. The WQIUL increased from a bad level of 7.35 to a good level of 60.58. Key indicators such as dissolved oxygen and the permanganate index approached their target values, demonstrating substantial progress in the lake’s ecological health. Furthermore, total phosphorus, ammonia nitrogen, nitrate, and suspended solids showed marked improvements, although they have not fully reached the desired targets. This case study underscores the effectiveness of composite water treatment strategies in rehabilitating small water bodies in educational environments. The findings highlight the potential for similar approaches to be implemented in other areas facing comparable environmental challenges, contributing to the broader field of sustainable water management.