Water is the most precious natural resource on our planet. Drinking water should be pure and free of contaminants to ensure proper health and wellness. The purpose of the present study was to analyze the microbial and chemical composition of potable tap water and compare it with that of Zamzam water. Water samples were examined using standard methods of analyses following the World Health Organization (WHO) and United States Environmental Protection Agency (EPA) for drinking water, with respect to total dissolved solids (TDS), electrical conductivity (EC), pH, concentrations of calcium, magnesium, potassium, sodium, chloride, fluoride, sulphate, and nitrate. The two sources of water were examined for the presence of potential pathogens, which include viable counts for total viable bacterial count (TVB) and presence of coliform in water. The isolated strain of drinking water approved to be of family Enterobacteriaceae by the most probable number (MPN) technique. Suspected colonies were confirmed and identified as E. coli by cultural, morphological, staining characteristics and biochemical identifications. E. coli isolate was tested for its resistance to ten different antibiotics by the disc diffusion method. Also, the occurrence of filamentous fungi together with bacteriological parameters was assessed in this study, Aspergillus spp. was the most frequently isolated fungal species. The data suggested that the drinking water quality deterioration in Alexandria was unpalatable due to poor sanitation and unawareness about personal hygienic practices. On other hand there wasn't any sign of microbiological growth for Zamzam water samples and free from any contaminant. Keywords: Potable tap water, Zamzam water, Microbial water quality, E. coli, physicochemical analysis.