The designation "ocean water" refers to water molecules collected directly from the ocean, rather than from other points in the water cycle (e.g., rain, snow, river or lake water). Water from different points in the water cycle contains molecules with differing ratios of isotopes due to the slight differences the isotopes cause in the rates of evaporation and condensation. VSMOW is not a standard for seawater, which contains other molecules in addition to water molecules. Fresh distilled VSMOW is used to make high accuracy measurements of water's physical properties and to produce laboratory standards.