High Quality Content by WIKIPEDIA articles! Vapor quality is a quantitative description of the usefulness of a vapor to do work. Steam engines use water vapor (steam) to drive pistons which effects work through movement. The quality of steam can be quantitatively described.Steam quality (steam dryness) is the proportion of saturated steam in a saturated water/steam mixture. A steam quality of 0 indicates 100% water while a steam quality of 1 (or 100%) indicates 100% steam. Steam quality is very useful in determining enthalpy of saturated water/steam mixtures since the enthalpy of steam (gaseous state) is many orders of magnitude higher than enthalpy of water (liquid state).