The sustainability of the environment and human health depend on the quality of the water. In this study, drinking water from rivers, municipal sources, and commercial bottled brands in various UK regions—including London, Manchester, and Scotland—will be thoroughly assessed for its chemical, physical, and microbiological characteristics. More than 17 different types of studies were carried out using a combination of field sampling, laboratory testing, and data visualization tools (Python and Power BI). These analyses ranged from heavy metals and microbiological presence to pH, turbidity, and dissolved solids. Digital probes, agar cultures, nutrient broth enrichment, and test strips were used to test water samples. The findings showed considerable regional and source-specific differences: While Manchester and several areas of London showed high levels of bacterial contamination, particularly in tap and river water, Scotland’s freshwater was of the highest quality. Remarkably, microbiological residues were found in even bottled water brands like Kirkland and Evian. This study draws attention to hidden health concerns, especially those posed by infrastructure and industrial runoff, and highlights notable disparities in water safety throughout the United Kingdom. This study’s tri-source comparison, multi-parameter testing, and geographical mapping of potability hazards are innovative; they close a significant gap in the literature on UK water quality and help upcoming policy and treatment advancements.