Abstract: The present study was conducted to determine groundwater chemistry, ascertain quality of water for various uses (domestic and agriculture) and define recharge sources of environmental isotopes in Wadi Malal, Al-Madinah Al-Munawarah, Saudi Arabia. Evaluation of water quality revealed that salinity and nitrate concentration are much higher than the established standards for various uses (so to say: irrigation and drinking etc.). Generally, the groundwater has been salinized by the equilibrium of infiltrated rainwater with slight soluble minerals in the regolith and evapoconcentration of groundwater that has been used for irrigation. Well waters in Wadi Malal along its flow path are too saline and the nitrate levels are too high to be used as drinking water. The salinity and sodicity levels in about 80% of the surveyed well waters are sufficiently high, when used for irrigation, to pose constraints on soil, crop and water management. Based on the concentration of the environmental isotopes (Deuterium and Oxygen-18) coupled with different ratios of NO3/Cl and HCO3/Cl, the primary source of the groundwater is rainfall that has occurred during the last 100-200 years with slight fractionation process in the water system.