Equation

Equation

Range

Water class

Reference

2

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

<10

10 - 18

18 - 26

>26

Excellent

Good

Doubtful

Unsuitable

[21]

3

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

<20

20 - 40

40 - 60

60 - 80

>80

Excellent

Good

Permissible

Doubtful

Unsuitable

[21]

4

$\text{RSC}=\left[\left({\text{CO}}_3^{2-}+{\text{HCO}}_3^{-}\right)-\left({\text{Ca}}^{2+}+{\text{Mg}}^{2+}\right)\right]$

<1.25

1.25 - 2.50

>2.50

Good

Doubtful

Unsuitable

[21]