Groundwater Quality Determination for Drinking Purpose by Using Water Quality Index Technique: A Case Study of Gadap Town, Karachi, Pakistan

Present study is aimed at assessment of groundwater quality of Gadap Town for drinking purpose using water quality index (WQI) technique. Gadap is located in the outskirt of Karachi city and mainly influenced by the agriculture activities. Groundwater samples (n = 22) were collected mainly from boring wells and a few through tube wells from variable depths (100-600 feet). The analytical results of water reveal occurrence of very high TDS (range: 466-3810; mean: 1402) and hardness contents (range: 250-2800 mg/L). On the other hand, pH varies (range: 6.9-8.1; mean: 7.5) within WHO guidelines (6.5-8.5) with a few samples showing turbidity. About one third of total collected samples (n = 8) were analyzed for qualitative determination of microbial contamination which are found positive, except one sample, indicating the sewage mixing. Major chemistry of groundwater is also found disturbed in terms of high content of Na (mean: 219 mg/L), K (mean: 15 mg/L), Ca (mean: 144 mg/L) and Mg (mean: mg/L 137). Similarly, anions varied in the order of Cl > HCO3 > SO4 > NO3. Although some parameters show the bad quality of water but Water quality index (WQI) value (16.18) indicates that the groundwater quality is suitable for drinking purpose. It is inferred from the present study that water quality is partly polluted due to anthropogenic activities mainly by sewage infiltration