Initial water deposition on the moderately reactive precious metal surface Ru(0001) has been thought to produce an ice-like bilayer. However, calculations from first principles show that the wetting layer observed on Ru(0001) cannot be formed of undissociated water molecules. An energetically favorable alternative, consistent with the remarkable observation that the wetting layer's oxygen atoms are nearly coplanar, is a half-dissociated monolayer wherein water molecules and hydroxyl fragments are hydrogen-bonded in a hexagonal structure and hydrogen atoms bind directly to the metal.