| Summary: | This paper assesses the chemistry of groundwater and evaluate its quality for drinking purpose using water quality index (WQI) approach and comparing to WHO and Ethiopia water quality standards in Adigrat area in Tigray, northern Ethiopia. Chemical composition of the groundwater in the area varies widely depending on the human activities. A total of 22 depth integrated groundwater samples were collected from 13 boreholes, 4 shallow, 4 hand-dug wells in addition to 1 reservoir, using purposive sampling technique. These samples were analyzed for physico-chemical parameters which include cations (Sodium, Potassium, Calcium, Magnesium, Iron, Manganese, Chromium, copper and Ammonia), anions (Fluoride, Chlorine, Nitrate, Nitrite, Bicarbonate, Sulphate and Phosphate) and other parameters (total hardness, hardness as calcium carbonate, Alkalinity pH, electrical conductivity, Total Dissolved solids) as well as physical parameters (turbidity, true color, odor and taste), were assessed to evaluate the groundwater quality for drinking.The groundwater is suitable for drinking purpose with respect to pH, EC, TDS and CaCO3 hardness as well as physical parameters (turbidity, true color, odor and taste). However, total hardness, iron, calcium, magnesium and chromium, the groundwater needs water treatment for quality adjustment. It is also suitable for drinking purpose taking into account all anionic concentrations (SO4−2, PO4−2, NO3−2, NO2−, Cl−, F− and HCO3−). Generally, the cations, anions and the chemical parameters (total hardness, Calcium hardness, Alkalinity pH, electrical conductivity, Total Dissolved solids), are high around the town and old waste disposal sites as well as in cultivated agricultural fields where point and non-source of domestic, factories as well as fertilizers beside the nature sources.With respect to water quality index, 95.45% of the samples indicate that, the groundwater is classified under excellent where as 4.55% of the samples reflect the groundwater is poor and unsuitable class as far water quality index is concerned. According to water quality index guideline (Chaterjee and Raziuddin, 2002), the groundwater is suitable for drinking use generally with some restrictions. The objectionable groundwater is restricted around the town with main of contaminants domestic and factories wastes. The hydrochemical data reveal that the groundwater of the study area consists of six hydrochemical facies, (Ca–Mg–HCO3–SO4, Ca–SO4–HCO3, Mg–Ca–SO4–HCO3, Ca–Mg–SO4–HCO3, Mg–Ca–HCO3–SO4 and Ca–HCO3–SO4). Keywords: Groundwater, Drinking, Hydrochemistry, Quality, Adigrat, WQI
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