The hardness of 10,000 Litres of hard water sample was completely removed by passing it through a zeolite softener. The zeolite softener required 5000 litres of NaCl solution containing 1170 mg of NaCl/litre. Determine the hardness of water sample.

1170 mg of NaCl → 1 litre

∴ 5000 litres solutions contains → 5000 X 1170 = 5850000 mg of NaCl

Now, CaCO3 equivalent $= 5850000 X \frac{100}{2 X 58.5} \\ = 5 \times 10^6 \ \ mg \ \ of \ \ CaCO3 \ \ equivalent$

$1 litre → 5 X {10}^6 \ \ ppm \\ 10^4 litre → x \\ ∴ x = 5 X 10^6 X 10^4 $

Hardness of water sample = 5 X $10^{10}$ ppm