Something that's drinkable can be swallowed safely without causing harm.
When we talk about water being safe to drink, we often say it's potable. But if someone asks if a particular brand of soda is drinkable, they mean can you actually finish it or does it taste so bad you won't touch it? It might sound silly, but sometimes you'll read reviews and people will complain that some beers are too bitter to be drinkable. They don't mean the beer's poisonous or anything; just that it tastes really unpleasant.
(chiefly in the plural) That which can be drunk.
Able to be drunk (as liquid).
