In several areas like water desalination and geothermal applications, the occurrence of silica in the used waters is undesirable. Many studies show the complexity and the diversity of the topic, For a better understanding of some of its analytical aspects the determination of amorphous silica content of natural waters, was carried out by various analytical methods, Amorphous silica solubility, at different temperatures, pH and ionic strength was studied. The heat of silica dissolution and the activity coefficient of dissolved silica were determined. A microcomputer program with the LabView graphical language was designed to calculate the solubility and concentration factors that indicate the limits above which silica precipitation occurs, This practical tool was applied to a variety of aqueous salt solutions acid to some brackish waters from South Tunisia, at different temperatures. Predicted solubility values, using deduced silica activity coefficient, are in good agreement with experimental results.