The density of water at 4°C is $1.0\times {10}^3{\mathrm{kgm}}^{-3}$ The volume occupied by one molecule of water is approximately $\left(N_A=6.0\times {10}^{23}\right)$

1g water molecule volume = 1ml

$\frac{1}{18}$ mole water molecule volume = 1ml

1 mol water molecule volume  $\begin{array}{r}=\frac{1}{\frac{1}{18}\times 6.0\times {10}^{23}}\\ =3\times {10}^{-23}\mathrm{ml}\end{array}$