A sampling program was set up within North Al-Hail to determine the presence and extant of bacterial regrowth in household storage tanks. Control samples from the main pumping station and different sites of the distribution system before the water entered the household system were analyzed to ensure the integrity of the system. A total of 120 water samples collected from 30 houses were analyzed for microbial quality including the identification of isolated microorganisms and characterization of physical and chemical parameters. The houses were selected so as to represent the main water storage tanks used, which are Glass-reinforced plastics (GRP), Polyethylene (PE) and steel. In parallel, a comprehensive questionnaire was conducted and 50 houses within the studying site were surveyed. Also, ten storage tank manufactures were surveyed to ensure suitability of materials used for constructing the tanks. Water sampling was performed such that to include the following sites: main water column, kitchen tap, bathroom taps and garden taps. Also, samples of product water were collected when home treatment devices were available. Biofilm deposits from inner wall and inner faces of taps and showerheads were swabbed. Water samples were analyzed for total heterotrophic microbial populations, whereas swab samples were checked for target pathogens, which were Aeromanas, Pasteurella, Pseudomonads, Yersinia and Salmonella. An attempt to isolate Legionella was also carried out. The highest HPC number was found in steel tanks along with high frequency of isolation of Aeromonas spp suggesting the suitability of Aeromonas as an indicator of microbial quality in storage tanks. In these tanks low Pseudomonas counts was detected wherease high counts were found in plastic tanks (GRP and PE) along with low HPC numbers and Aeronomas suggesting the intibitory suppression of Pseudomonads on heterotrophic bacterial populations. High General Stress Response (GSR) was found among Pigmented bacteria isolated from steel tanks. High total coliforms was found in GRP tanks in paralled with isolation of enteric pathogens. No fecal coliform was isolated in all samples indicating the failure of E.coli as an indicator of pollution in storage tanks. Samples of product water showed one log increase in the total HPC and coliform count with the predominance of Klebsiella and Enterobactor spp. Analysis of biofilm indicates little quantitative or qualitative uniformity. All target organisms were isolated from GRP tanks. Frank pathogens were less frequently isolated compared to opportunistic pathogens. Antimicrobial susceptibility test revealed emergence of resistant strains among the frequent isolates of biofilm populations. In addition, Legionella spp. Were isolated from GRP tanks only where algal colonization was observed. These results suggested after growth event in the storage tanks compared to negative results obtained from control samples. Most of physical and chemical parameters were found to meet current quality standards. High turbidity was detected in steel tanks which paralleled high yeast and molds counts as well as presence of algae. Low free chlorine residual was in GRP tanks as biofilm formation was high and exerted chlorine demand. Information gathred from field survey of storage tanks manufactures revealed non compliance with manufacturing standards especially in GRP tanks. Materials used for construction were found health hazardous and many manufacturing defects were observed during inspection, which were noticed also by consumers. Handling of the tanks during installation was found to be of great importance to minimize sources of contamination. Public awareness is needed to educate consumers about proper maintaince of water storage tanks to minimize microbial after growth