$\mathrm{BeO}$ and $\mathrm{Be}{\left(\mathrm{OH}\right)}_2$ are water-insoluble. But, $\mathrm{BeO}$ is soluble in basic as well as acidic solution as it can react with both acid and base i.e. it is amphoteric. The explanation for its amphoteric behaviour is the partial covalent character of the $\mathrm{Be}-\mathrm{O}$ bond. Also, due to small size and $+2$ charge on ${\mathrm{Be}}^{2+}$  ion, it can react with ${\mathrm{OH}}^{-}$ from base and ${\mathrm{O}}^{2-}$ can react with ${\mathrm{H}}^{+}$ from acid.