Groundwater is one of the most valuable resources in Oman. Al-Seeb city is one of the most cities storing groundwater. The rapid residential activities took place during the last 15 to 20 years, especially in the South East of AlSeeb until it became one of the most congested cities across the country. The buildings have been designed and built with septic tanks as a basic sewage system. Many of these septic tanks are very old and outdated. Furthermore, many of them have not been built according to the required specifications, which resulted in the leakage of wastewater through the soil to the groundwater. This research study aims at studying the effects of septic tanks leakages on groundwater quality in south east of Al-Seeb area. Seven different drinking water wells have been selected to evaluate the quality of the groundwater. The results were compared with the drinking water standard's. Five visits were conducted to each well between February and October 2013. Samples were collected and analysed for different water quality to evaluate the risk on environment and public health due to wastewater leakages from the septic tanks. Tests include microbiological test, biochemical oxygen demand (BOD), pH, electrical conductivity (EC), turbidity, alkalinity, hardness, total organic carbon (TOC), anions (Fluoride, Chloride, Bromide, Nitrate, Sulphate), and cations (Sodium, Potassium).. The obtained results showed elevated values of specific tests such microbial test (coliform bacteria reached 200 MPN per 100 ml in some cases), BOD (reached 10 mg/l in some cases), TOC (reached 100 mg/l in some cases) and nitrate (exceeded 100 mg/l in some cases) indicated possible contamination due to wastewater. However, this problem needs more detailed studies to collect sufficient data to reach solid conclusions. Consequently, appropriate recommendations and action plans can be taken to prevent and alleviate this long term problem.