Municipal Solid Waste (MSW) landfills play a pivotal role in waste management (WM), but they also introduce a spectrum of environmental challenges and risks. The study focuses on the issues of water quality and leachate chemistry changes at landfill sites. Additionally, the study explores the efficacy of proper landfill design and reclamation measures. Through the case study of the Łubna landfill in Poland, the paper aims to provide knowledge of how the landfill operation may impact environmental conditions and contribute to the broader discourse on protecting water resources at landfill sites. The paper emphasizes the significance of monitoring to derive a holistic view of the ecological consequences of MSW landfilling. The results confirmed the importance and effectiveness of reclamation work at the old waste landfill, which had been operated for many years without taking into account the principles and premises of environmental protection. The findings from this study are expected to inform environmental policymakers, WM authorities, and researchers, offering valuable insights into the specific challenges posed by MSW landfill sites. Furthermore, this research serves as an example for understanding the broader environmental implications of landfill activities and reclamation, providing a foundation for sustainable WM practices.