Net profit is known as one of important indicators in evaluating companies and government agencies. In this study, causal effects in system dynamics and also econometric models is applied to investigate five sectors of water demand, population, hydrology, purification and financial resources. The model is developed and the impact of population and water demand on financial resources has been considered. Water and wastewater company revenue sources include: water sales, water supply and government funds (in exchange for its costs), including: human resources, water transfer and refinement, and etc. The results illustrated that demand side management of the water, in addition to decreasing demand for water, we can contribute more to the country's gross domestic product (GDP). In other words, we have a larger share of GDP.