Given the ever-increasing demand for water and the limitation of sources of rising freshwater supply, logical economic decisions and a more accurate assessment of water demand seem obvious. In this regard, relatively strong economic literature has emerged concerning water demand in agricultural, urban and industrial sectors. But with regard to the issue of transferability of water from one sector to another, there is a need for coherent studies to consider the total water demand for each of the three sectors. Therefore, the purpose of this study was to estimate the water demand function in agricultural, urban and industrial sectors in three cities of Mashhad plain, which is one of the prohibited plains of Khorasan Razavi province. In order to achieve water demand function in the agricultural sector of the three counties, a positive math planning model was used. After calibrating the 3 levels of the crop area, the water inventory of each city changed in 20 different scenarios and the price of shady water was obtained. Then, using the least squares method, a regression between the two variables of water inventory and the water shadow price of each city was estimated and the widths of the origin and gradient of water demand for each of these cities were thus obtained. Also, urban water and urban water demand functions in the study area were obtained using consumption values and prices per cubic meter of urban water per year, and with the help of price elasticity, the estimated demand in previous researches was 0.29. Given that the water demand function in the industrial sector is a function derived from production, in order to estimate the water demand function in it, the econometric approach of the production function was used, and from the information set of industrial workshops, 10 employees and more, the statistical center was used. For this purpose, three functional quadratic forms, Cobb-Douglas and Transfer were estimated for estimating industrial production function at the catchment area. In these patterns, the dependent variable of gross production of industrial units and independent variables including two variables of the Dviaghia index and the total amount of water consumed annually they were. The results showed that the Translog model was superior to the other two models. Finally, the industry\\\'s water demand stretched by 0.373.

Keywords