One who is overcome by thirst and drinks must make up the fast, but owes no expiation

Question: A man fasted in Ramadan, and his thirst became severe so he drank. What is the ruling?

Answer: He must make up the fast, and he owes no expiation, according to the more correct of the scholars' opinions. If he was lax in this matter, he must repent to Allah along with making up the fast.
As for the expiation, it is not obligatory except for one who has intercourse during the day of Ramadan, among those for whom fasting is obligatory; because the hadith was reported specifically regarding that.