Assessment of Bangladesh groundwater for drinking and irrigation using weighted overlay analysis

A weighted overlay analysis was conducted to calculate Water Quality Index (WQI) for drinking water using WHO and Bangladesh drinking water standards (BDWS) and for irrigation using irrigation water quality standards. The method used a normalized quality rating scale (qi) and relative weight (wi) for several water quality parameters to calculate WQI. This index-based suitability analysis was carried out to assess the overall water quality of groundwater in Bangladesh used for drinking and irrigation purposes. Drinking water quality index (DWQI) calculation was done based on As, Mn and hardness concentrations. For irrigation water quality index (IWQI) As, B, Cu, Fe, Li, Mn, Na, Zn and sodium adsorption ratio (SAR) were used. WQIs were calculated separately for the shallow tube wells (STW) (depth <150 m) and deep tube wells (DTW) (depth >150 m). The results revealed that 40.4% STWs and 88.7% DTWs have safe drinking water according to BDWS 57.6% STWs and 90% DTWs have safe drinking water based on WHO drinking water standards. Irrigation water quality index shows that 8.1% STWs and 23.1% DTWs have safe water quality. It has also been found that majority of deep tube wells have better water quality than shallow tube wells due to lower concentrations of contaminants in the deep tube wells compared to shallow tube wells. Some of the dissolved constituents in the groundwater of Bangladesh can potentially be great source of nutrients supplements required for plant growth. If the nutrients dissolved in groundwater replace the nutrients in fertilizers needed for plant growth, an average of US$12.61(BDT 1069) could be saved, which is approximately 19% of the total fertilizer cost.