Substitutional NaCl hydration in ice

${\mathrm{Na}}^{+}$ and ${\mathrm{Cl}}^{\ensuremath{-}}$ can replace water molecules in ice Ih with minimal lattice strain and without disrupting the crystal's H-bond network. First-principles calculations show that substitutional solvation is endothermic by as little as $0.49\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ per ion pair. Interstitial ion solvation is less favorable by $>1.5\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$.