Webel: Psy/MPsy: Psychrometrics for Mathematica: A suffix '$wat$i' indicates water (liquid or vapour) flow TO (into) the humid air mixture. A suffix '$wat$o' indicates water (liquid or vapour) flow FROM (out of) the humid air mixture.
Webel: Psy/MPsy: Psychrometrics for Mathematica: A suffix '$wat' indicates a water-related variable, quantity, or function (note that 'w' is reserved for the humidity ratio).