For the first time, the levels of some heavy metals in water in Alahsa farms, Saudi Arabia were examined. Three types of water were analyzed including groundwater, mixed water and wastewater. The total contents of Mn, Fe, Cu, Zn, Cd and Pb were determined using graphite-furnace atomic absorption spectrophotometry. The results obtained were verified through the analysis of a certified reference material, the results of which are in good agreement with the certified consensus values. As recommended by the Food and Agriculture Organization, the level of heavy metals in groundwater and mixed water have been found to be suitable for irrigation purpose. However, the occurrence of some heavy metals that discharged directly from man-made activities without treatment could result in some environmental problems in the future. On the other hand, the spatial distribution of Mn and Fe has been found to increase from southeast to northwest.