\(\frac{\partial}{\partial x}\left\{K\text{xx}\frac{\partial h}{\partial x}\right\}+\frac{\partial}{\partial y}\left\{K\text{yy}\frac{\partial h}{\partial y}\right\}+\frac{\partial}{\partial z}\left\{K\text{zz}\frac{\partial h}{\partial z}\right\}\)-W = Ss \(\frac{\partial h}{\partial t}\) (1)