Formulas Percentage of sodium $%\text{Na}={\text{Na}}^{+}+{\text{K}}^{+}/\left({\text{Ca}}^{2+}+{\text{Mg}}^{2+}+{\text{Na}}^{+}+{\text{K}}^{+}\right)\ast 100$ Equation (1) Sodium absorption ratio $\text{SAR}={\text{Na}}^{+}/\left[\left({\text{Ca}}^{2+}+{\text{Mg}}^{2+}\right)/\text{2}\right]$ Equation (2) Magnesium absorption ratio $\text{MAR}\left(\text{meq}/\text{l}\right)=\frac{{\text{Mg}}^{2+}}{{\text{Ca}}^{2+}+{\text{Mg}}^{2+}}\ast 100$ Equation (3) Residuel sodium carbonate $\text{RSC}\left(\text{meq}/\text{l}\right)=\left({\text{CO}}_{\text{3}}^{\text{2+}}+{\text{HCO}}_{3}^{-}\right)-\left({\text{Ca}}^{2+}+{\text{Mg}}^{2+}\right)$ Equation (4) Kelly’s Ratio $\text{KR}=\frac{{\text{Na}}^{+}}{{\text{Ca}}^{2+}+{\text{Mg}}^{2+}}$ Equation (5) Corrosivity Ration $\text{CR}\left(\text{mg}/\text{L}\right)=\frac{\frac{{\text{Cl}}^{-}}{35.5}+2\ast \frac{{\text{SO}}_{4}^{2-}}{96}}{2\frac{{\text{HCO}}_{3}^{-}+{\text{CO}}_{3}^{2-}}{100}}$ Equation (6) Permeabillity index $\text{IP}=\left[\left({\text{Na}}^{+}+{\text{HCO}}_{3}^{-}\right)/\left({\text{Ca}}^{2+}+{\text{Mg}}^{2+}+{\text{Na}}^{+}\right)\right]$ Equation (7)