This Letter shows that the ion-water (oxygen) distances for ions of monovalent, divalent and trivalent elements including lanthanides increase linearly with the covalent radii of atoms. The slopes and intercepts of the lines are found to depend on the Golden ratio. The ionic radii in water have been evaluated and ion/water boundaries located. The hydration distances of the oxygen of water to the peripheries of the cations are of four types and are constants. The distance of the hydrogen of water to the peripheries of halogen anions, which is the length of the 'hydrogen bond', is also a constant. (c) 2006 Elsevier B.V. All rights reserved.