ISABB Journal of Food and Agriculture Science Vol. 1(1), pp. 22-30, September 2011 Available online at http://www.isabb.academicjournals.org/JFAS ISSN 1937-3244©2011Academic Journals Full Length Research Paper Application of water quality index to assess suitablity of groundwater quality for drinking purposes in Hantebet watershed, Tigray, Northern Ethiopia Abraham Bairu Gebrehiwot 1 *, Nata Tadesse 2 and Elias Jigar 3 1 Research and Technology Development Directorate, Tigray Science and Technology Agency, Mekelle, Tigray, Ethiopia. 2 Department of Geology, Mekelle University, Mekelle, Tigray, Ethiopia. 3 Department of Natural Resources, Semera University, Afar, Ethiopia. Accepted 13 September, 2011 The study was conducted in Hantebet catchment area which has a total area of 24.5 km 2 with the major objective of assessing suitability of groundwater quality for drinking purposes through water quality index (WQI) investigation of the different hand dug wells in the watershed. This was done by subjecting the 20 groundwater samples collected to comprehensive physico-chemical analysis using APHA standard methods of analysis. For calculating the WQI, 10 parameters have been considered: pH, sodium (Na + ), potassium (K + ), magnesium (Mg 2+ ), calcium (Ca 2+ ), chloride (Cl - ), bicarbonate (HCO 3 - ), sulphate (SO 4 2- -S), nitrate (NO 3 - -N) and total dissolved solids (TDS). The WQI for these samples ranges from 54.41 to 86.24. All the groundwater samples estimated using the water quality index fall in the good water class and are all suitable for drinking purposes. Key words: Groundwater, water quality index, quality rating, weight, Hantebet. INTRODUCTION Groundwater is used for domestic and industrial water supply and irrigation all over the world. In the last few decades, there has been a tremendous increase in the demand for fresh water due to rapid growth of population and the accelerated pace of industrialization. Human health is threatened by most of the agricultural development activities particularly in relation to excessive application of fertilizers and unsanitary conditions. Rapid urbanization, especially in developing countries like India, has affected the availability and quality of groundwater due to its overexploitation and improper waste disposal, especially in urban areas (Ramakrishnaiah et al., 2009). Intensive irrigated agricultural discharges into the groundwater can bring about considerable change in the groundwater quality. These anthropogenic activities on the groundwater pose serious threat to the groundwater users. Once the groundwater is contaminated, its quality *Corresponding author. E-mail: abrahambairu@ymail.com, AbrahamBairu@gmail.com. Tel: +251-914-733028, +251-914- 004676. cannot be restored by stopping the pollutants from the sources. It therefore becomes imperative to regularly monitor the quality of groundwater and to device ways and means to protect it. Water quality index (WQI) is one of the most effective tools to communicate information on the quality of water to the concerned citizens and policy makers. It, thus, becomes an important parameter for the assessment and management of groundwater. WQI is defined as a rating reflecting the composite influence of different water quality parameters (Ramakrishnaiah et al., 2009). The study area, Hantebet catchment, is found in the Southeastern Zone of Tigray, Seharti-Samre Woreda that has a total population of 61,945 males, 62,545 females and a total population of 124,499. Seharti-Samre has total area coverage of 1538.74 km 2 where the density of population living per square kilometer is 80.70 (FDRECSA, 2008). Specifically, Adiss Alem tabia in which the study area is found consisting of four kushets, namely: Atsgebta where the tabia administration and agricultural bureau is found, Gonekat, Hantebet, kushet and Astah. The total population size of the tabia is 8109, which is