In the south Mediterranean countries and especially the North Africa, the water demands, since many decades, have increased while the conventional water availability has decreased dramatically. These trends continue. The obligation to use other non-conventional water resources such as desalinating water or waste water reuse becomes a necessity. Nanofiltration is a membrane process that competes with reverse osmosis for desalination and the removal of specific inorganic contaminants. The focus of the present study is to compare the performances of Nanofiltration membranes for the desalination of the brackish waters in heavily loaded in sodium and chloride contents and to simulate the maximum of the number of modules in pressure tube using the pressure tube configuration. Three commercial NF membranes were tested at different running conditions such as (pressure and type of configuration). The tested parameters were: Salt rejection (TDS), chloride, sodium, Flux rate (L/m.hr), permeability (L/m2.hr.bar) and Flux recovery rate.