Source : Webster's Revised Unabridged Dictionary (1913)

Drinkable \Drink"a*ble\, a.
   Capable of being drunk; suitable for drink; potable.
   --Macaulay. Also used substantively, esp. in the plural.
   --Steele.

Source : WordNet®

drinkable
     adj : fit to drink [ant: {undrinkable}]
     n : any liquid suitable for drinking; "may I take your beverage
         order?" [syn: {beverage}, {drink}, {potable}]