Evaluation of drinking water quality variation in Urmia plain using Integrated Water Quality Index (IWQI)

There are different factors involved in water quality and it’s difficult to study all of these factors to assess water quality. Quality indexes are a powerful tool for conclusion and comparison groundwater quality. The current study investigates the integrated water quality index (IWQI) with the Kriging geostatistical technique for the Urmia plain between 2002 and 2011 over a period of ten years. Physicochemical parameters including acidity (pH), electrical conductivity (EC), total dissolved solids (TDS), and ions of calcium, magnesium, sodium, potassium, chloride and sulfate have been used to calculate the index. For different years, 63 groundwater samples were used to calculate the IWQI index and compared with other indexes such as %Na and sodium adsorption ratio (SAR). The results show that most parts of the Urmia plain are in the middle and good class in terms of IWQI classification. Also, the quality in 2004 is better than previous years and the most unsuitable quality is related to 2010. The study of spatial variations of the IWQI indicates the lower quality of the southern parts of the plain than other parts, especially the center part of the plain. As the southern parts of the plain in terms of IWQI classification is often in the middle class, and in 2010 with the decrease in the quality of the entire plain, the southern parts have also decreased to a lower quality class. The center parts of the plain are in a better condition than other parts, especially in 2004, when the quality of the middle class improved to an excellent level. The quality of the northern parts of the plain in terms of IWQI is often in the good class, so that in some years it has changed to the middle class and in 2010 to the poor class.