In this research, the quality of drainage water was studied by using the water quality index (WQI). Water samples were taken from the Al-Dujaila River and Al-Dujaila drainage. Drainage water was diluted to different ratios with river water to decrease its salinity and increase its potential for agricultural uses. The diluted samples contained between 0 and 100% drainage water, and between 100 and 0% river water, in 10% steps – i.e., 0:10, 1:9, 2:8, 3:7, 4:6, 9:1, 8:2, 7:3, 6:4, and 5:5. After dilution of water, chemical properties, ion activities, electrical conductivity (EC), soil reaction (pH), sodium (Na+), calcium (Ca+2), magnesium (Mg+2), and total dissolved solid (TDS)) were measured in the laboratory of the University of Wasit/College of Agriculture, for computing the drainage water quality index (DWQI), sodium adsorption ratio (SAR), exchangeable sodium percentage (ESP), and soluble magnesium percentage (Mg%). Mathematical models were generated to predict the DWQI using DataFit software, depending on the water's chemical properties, and to find the best dilution ratio, which was 9:1. Model 2 includes the DWQI with SAR, ESP that gave the best results (R2 = 99.99%, RE = 0.0007, MAE = 0.425, RMSE = 0.6, and SEE = 1.992). The diluted drainage water used in this study was not suitable for either irrigation or human use.

  • Quality of diluted drainage water.

  • DWQI, SAR, ESP, and Mg%.

  • Mathematical models and DataFit software to predict DWQI, and determine the best dilution ratio.

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