Groundwater Valuation Using Residual Method and Considering Water Salinity in Varamin County

The economic value of water is one of the most important factors for allocating water among various consumptions and encouraging users to take necessary actions to increase investments related to improving water productivity. There are several methods for economic valuation of water. In this study, due to the key role of water in irrigation of agricultural products, residual valuation method was used for agricultural wells in Varamin County, with a wide range of water salinity. The average economic values of water for cucurbits, wheat, barley, and alfalfa were 2513.1, 5334.5, 1424.6 and 5647.6 Iranian Rials per cubic meters (IRR.m-3), respectively. The exchange price of water among the farmers in the study area was calculated as 5231.8 IRR.m-3, which was close to the calculated residual value for wheat and alfalfa crops. The coefficient of determination (R2) for the relationship of economic value and salinity of irrigation water for the above crops was 0.806, 0.878, 0.932, 0.911, and 0.702, respectively, which indicates that the main changes of economic value of water is related to salinity of water. According to the relationship between salinity and irrigation water value in the study area, the residual value of water was zero in the electrical conductivity of 3.61, 7.30, 5.20, and 8.24 dS.m-1 for cucurbits, wheat, barley, and alfalfa, respectively. As a result, the water pricing policy in the study area should be such that for water salinities higher than the mentioned values, the selling price of water is set lower than the current value, so that the farmers do not suffer losses. Another option is that choice of crop should be based on greater resistance to salinity and its economic value.