Recognize that other ions like $\mathrm{K^{+}}$, $\mathrm{Ca^{2+}}$, $\mathrm{Mg^{2+}}$, $\mathrm{NO_3^{-}}$, $\mathrm{SO_4^{2-}}$, and $\mathrm{HCO_3^{-}}$ are present but in much smaller concentrations compared to $\mathrm{Na^{+}}$ and $\mathrm{Cl^{-}}$.