An Economic Study about the role of both of direct foreign investment and BOT System (Build Operate Transfer) on treating the water gap appeared in the Egyptian water balance as a result of the population increase while Egypt's share of Nile Water remains fixed. Such treatment shall be implemented by creating untraditional water resources to achieve the principles of sustainable development. It depends on recycling sewage water by treatment and on seawater desalination. In addition, such thesis studies the mechanism of applying the direct foreign investment in desalination projects of seawater and wells with high salinity as well as its role in financing the three-stage sewage water treatment projects. Besides, such thesis studies the mechanism of applying BOT System on desalination projects of seawater and wells with high salinity and its role in financing the three-stage sewage water treatment projects as well. The thesis depended on the use of the inductive approach, (the reference survey of the previous studies), the descriptive analytical approach (describing the technical methods used in desalination and the technical methods of the three stages of treatment), and the quantitative standard approach by using the statistical model for selecting the intangible relationship to test the nihilist purpose of the dependent variable which is the foreign finance in the infrastructure).   The results of this thesis were as follows: 1) The correlation between Potable water desalination sector and the direct foreign investment (0.324) indicates the existence of a contribution for the direct foreign investment such relation needs to be activated in a more active manner. 2) The relationship between Sewage water treatment sector – whether two-stage treatment or three – stage treatment – and the direct foreign investment is very weak (0.0248). There are no plan or attraction factors provided by the Egyptian party to attract the investments through the financing plans of this sector projects. 3) The correlation between Seawater desalination sector and BOT System (0.006) is in an absence state regarding the contribution. Such independent variable can be considered from the quick financing factors. 4) There is no correlation between the use of BOT System (0.006) and two / three stage sewage water treatment projects.