The degradation of surface and groundwater quality significantly impacts environmental sustainability and public health. Water quality is vital for human use and achieving Sustainable Development Goals. However, groundwater contamination often hinders progress due to resource limitations for adaptation. This chapter examines natural and human-induced contamination sources, processes, and impacts on surface water and underground aquifers. Key contamination sources include industrial effluents, agricultural runoff, urban wastewater, and natural substances, introducing pollutants includes heavy metals, nutrients, pathogens, and organic chemicals into water systems. The chapter outlines contamination pathways, noting that point-source discharges typically pollute surface waters, while groundwater pollution occurs through leaching and infiltration from diffuse sources. Large-scale groundwater quality assessments are scarce compared to surface water and often rely on inadequate data. Contaminated water leads to biodiversity loss, ecosystem damage, and health risks. The chapter underscores the importance of comprehensive water quality management, encompassing advanced detection and remediation technologies, robust regulatory frameworks, and sustainable land use practices. It emphasises the need for multidisciplinary collaboration to effectively tackle the complexities of water contamination and protect water resources.