Can I leave without paying?

I don’t know the answer to this so perhaps others can enlighten me.

At what point during the eating at a restaraunt experience is it ok to leave without paying? For example, If I order my drink but haven’t gotten it yet and then have an emergency call on my cell phone and have to leave do I still pay for the drink? what about after ordering the meal but before getting it? I mean of course if they brought you anything besides water you should obviously pay for it, but are you responsible for paying as soon as the meal is ordered or not until it is delivered?