Tetragonal iron selenide (β-FeSe) adopts the simplest crystal structure of the recently-discovered iron-based superconductors, and is of considerable interest for the development of the structure-properties relationship. Conventional solid state syntheses produce samples with superconducting transitions near 8 K, though these methods require extended treatment at high temperatures and are undesirable for large-scale applications. Additionally, many of these samples have homogeneity ranges, and include various impurity phases. Several low-temperature solution-based syntheses have been reported, though samples produced by these methods exhibit antiferromagnetic ordering instead of superconductivity. We have developed a solvothermal method to synthesize phase-pure β-FeSe from elemental precursors at low temperatures (200 °C). We have shown how the superconductivity can be triggered in those samples depending on the synthetic conditions. Characterizations of the superconducting and non-superconducting samples by means of synchrotron X-ray powder diffraction and neutron diffraction pair distribution function (PDF), TEM, and 57Fe Mössbauer spectroscopy reveal complex interplay between Fe vacancy formation, incorporation of the interstitial hydroxyl groups, structural distortion, and superconductivity.