Excess amount of solid calcium sulphate (CaSO\(_4\)) was added to a pure water sample (pH = 7) so that some solids remain undissolved at the equilibrium. The solubility product of CaSO\(_4\) is \( 2 \times 10^{-5} \, \text{mol}^2/\text{L}^2 \). The molar concentration of SO\(_4^{2-}\) in this water sample at equilibrium will be _______ mol/L (rounded off to three decimal places).