In this research paper, the physical, chemical, and biological characteristics of drinking water which is supplied to the housing complex in Tikrit University –Iraq were studied. Five sites were selected in the housing complex and have been testing within three months for the period from 1/12/2011 to 26/2/2012 with five tours or runs during this period. The results showed high concentrations of some quality characteristics in supplied drinking water such as turbidity which was 192NTU in one of these sites as well as the presence of biological contamination is recorded a high concentration of pathogenic bacteria which was 109 MPN/100 ml in another site. Also the results showed that the concentration of residual chlorine was less than accepted limited which was 0.1 mg/l. Besides the results showed that the drinking water is very hard. Statistical analysis was conducted and the results showed high correlation R² = 1 between the dependant variable (MPN) and independent variables temperature, pH, turbidity, and TDS). The results showed that the calculated Langelier Saturation Index, LSI was negative and thus corrosion of iron pipes and metal parts in the water distribution system may occur.