The equation of moisture retention curve is a non-linear relation to the water content. Since the moisture retention curve can only be determined experimentally, its true behaviour in practice is only known at a finite number of points. Two methods to obtain values at non-experimental points can be used. The best and most obvious method is by interpolation, but this method can only be successful in those cases where the experimental points are closely spaced. The most recent approach fits an equation to the experimental points. The equations commonly used are the Brooks and Corey function and the Van Genuchten (1980) function. According to Van Genuchten, the moisture retention curve may be expressed as,