Prof. S.K Gunatilake
Mr. Udara Piyathilake - Sabaragamuwa University of Sri Lanka
Sri Lanka is characterized by well-demarcated climatic zones known as the wet zone, intermediate zone, and dry zone based on the rainfall variability. Groundwater in these climatic zones is extensively utilized for drinking purposes by 80% of the population in the country. Therefore, it has become necessary for systematic assessment and monitoring of groundwater quality variability in different climatic zones to examine its suitability for drinking and to adopt appropriate measures for protection.
Thus the prime objective of this study is to develop a water quality index (WQI) to investigate the water quality variability in three climatic zones. A total of 256 groundwater samples were collected representing three climatic zones and analyzed for their pH, Electrical conductivity, major anions viz. nitrate, phosphate, sulfate, fluoride, chloride, and major cations viz. sodium, magnesium, potassium, and calcium. Ultimately the weighted arithmetic WQI method was applied based on the recommended guidelines for drinking water quality by the SLS 614:2013 (Sri Lankan Standard) for drinking purposes. Furthermore, the computed WQI values were classified into five categories as excellent (0 – 25), good (26 – 50), poor (51 – 75), very poor (76 – 100), and unsuitable (>100). The results revealed that 96% of samples collected from the wet zone are categorized under excellent or good water quality categories whereas only 4% of water samples are categorized under poor water quality category. However, in the intermediate zone, 61% of groundwater samples are categorized under excellent or good water quality categories whereas 39% of samples are categorized under poor to unsuitable water quality categories. In the dry zone, 56% of groundwater samples were categorized under excellent or good water quality categories whereas 44% of groundwater samples were recorded as poor, very poor, or unsuitable for drinking purposes. Thus, the results indicate a clear difference in the groundwater quality between climatic regions.
Furthermore, the results indicated that WQI has a strong positive correlation (0.9) with fluoride levels of groundwater. Therefore it can be inferred that fluoride is the key contaminant that pollutes the groundwater in intermediate and dry zones. Moreover, these results can be effectively used by researchers for further studies and decision-makers can use these results for groundwater quality management activities in different climatic zones in Sri Lanka.