Remodeling of the WQI Index for the evaluation of the Shkumbini River’s water quality in Albania using the statistical method

Nowadays, assessing the extent of natural water resources and making an accurate assessment of its quality is a task as important as it is urgent. The determination and assessment of the Water Quality Index (WQI) is a method used in our paper to assess the water quality of the Shkumbini River in Albania - one of the main rivers of our country. We used the analysis of the WQI index, because it is the most optimal analysis we can do with the collected data and because it is an easier index to interpret. WQI is considered fundamental information for analyzing and demonstrating the water quality. We have used the data collected during a 4-year period from the Shkumbini River's water (in total 72 sets of data) and through the statistical method of Multiple Linear Regression (MLR) we have defined an equation for the assessment of WQI expressed by three variables: biological oxygen demand, hydrogen carbonate and phosphorus (BOD, HCO3, P-total). MLR is implemented by interpreting the correlation coefficient R2 , which demonstrates that 99.6% variability of the data is explained by the new regression equation. The t-test was also used, demonstrating the equivalence of the WQI index, calculated from the newly constructed equation, and the values of the first WQI, calculated using nine variables. The reduction of the number of determining variables of WQI has its advantages, both financially, as well as from the way that the water quality of the Shkumbini River is interpreted and monitored.