Indices

Formula

Reference

Percentage Sodium, Na%

$\%\text{Na}=\frac{{\text{Na}}^{+}+{\text{K}}^{+}}{{\text{Na}}^{+}+{\text{K}}^{+}+{\text{Ca}}^{2+}+{\text{Mg}}^{2+}}\times 100$

Wilcox (1955)

Kelly Ratio, KR

$\text{KR}=\frac{{\text{Na}}^{+}}{{\text{Ca}}^{2+}+{\text{Mg}}^{2+}}$

Kelley (1940)

Magnesium Absorption Ratio, MAR

$\text{MAR}=\left(\frac{{\text{Mg}}^{2+}}{{\text{Mg}}^{2+}+{\text{Ca}}^{2+}}\right)\cdot 100$

Szaboles & Barab (1964)

Total Hardness, HT

TH (CaCO₃) mg/L = 2.5 Ca²⁺ + 4.1 Mg²⁺

Todd (1980)

Residual Sodium Carbonate, RSC

$\text{RSC}=\left({\text{CO}}_3+{\text{HCO}}_3-\left(\text{Ca}+\text{Mg}\right)\right)$

Eaton (1950) and Raghunath (1987)

Sodium Absorption Ratio, SAR

$\text{SAR}=\frac{\text{Na}}{\sqrt{\frac{\text{Ca}+\text{Mg}}{2}}}$

Richards (1954)

Permeability Index, PI

$\text{PI}=\frac{\left(\left(\text{Na}+\text{K}\right)+\sqrt{{\text{HCO}}_3}\right)\ast 100}{\text{Ca}+\text{Mg}+\text{Na}+\text{K}}$

Doneen (1962)

Water Quality Index, WQI

$\text{WQI}={\displaystyle \sum _{i=1}^n{W}_i{q}_i}{\left[{\displaystyle \sum _{i=1}^n{W}_i}\right]}^{-1}$

Sisodia & Moundiotiya (2006)