Start by converting your anion and cation concentrations to milliequivalent percentages.

Create 4 excel columns 1 each for HCO3 +CO3(weak acid anions), Cl+ SO4 (strong acid anions), Ca+ Mg and Na + K

Then create 2 additional columns for

1.(HCO3+CO3)-(Cl+SO4)

2. (Ca+Mg)-(Na+K)

Plot a cross plot with 1 above on the vertical axis and 2 on the horizontal axis.

You can do this with excel but origin 8 will give you a better result

I hope this helps.