My suggestions:
"I have this incredible craving for a nice, long, tall glass of mineral water right now!"
"I'm a vegan - Can you guarantee to me that that whiskey is certified 100% vegan?"
"My father-confessor gave me the penance to abstain for three weeks - this is my second day!"
"Am on an antibiotic regime right now - not allowed to drink!"
"Sorry: Lost a bet. Have to stay on the wagon for two more months!"
Regards,
“Oh thanks! But I don’t drink.”