Indiscriminate dumping of wastes at any available space within the vicinity of residential quarters is a common practice in many developing countries like Nigeria. The negative environmental impacts of waste dumpsites have continued to generate public health concern. In this study, the impact of waste dumpsites on the physicochemical and microbiological qualities of underground water sources located within their vicinities in Delta State, Nigeria, were assessed using standard biochemical techniques. A total of 45 water samples were collected from hand dug wells in Warri, Agbarho and Agbor (all in Delta State) at distances of about 500m, 1km and 1.5 km radius of dumpsites and analysed for physicochemical and microbiological quality using the ASTM and standard microbiological techniques respectively. The results revealed that all the analyzed parameters decreased with distances away from the dumpsites. The physicochemical parameters such as turbidity, dissolved solid were significantly (P<0.05) above the WHO regulatory limits at ≤ 1km radius of most dumpsites. The total heterotrophic bacteria count, which ranged between 2.1 × 10 3 to 6.52 × 10 6 cfu/ml, was also significantly (P<0.05) higher than regulatory limits. Findings from this study suggest that waste dumpsites could impact negatively on the microbial and some chemical qualities of hand dug well waters sited in their vicinities. Hence, the location of dumpsites at least 1km distance away from residential quarters as well as simple boiling and filtration treatment of drinking water sources in the study areas are recommended.