The network motif of water, vitrite, is introduced to elucidate the intermediate-range order in supercooled liquid water. Unstrained vitrites aggregate in supercooled liquid water to form very stable domain. Hydrogen bond rearrangements mostly occur outside the domain, so that the dynamical heterogeneity also stands out. Pre-peak in the structure factor of low density amorphous ice is reproduced by inter-vitrite structure factor. The vitrite can therefore be regarded as a plausible building block of the intermediate-range order and heterogeneity in supercooled liquid water and low-density amorphous ice.