Question

A person gargled and a little bit of water enters into him (i.e. his belly, down his throat etc.); is his fasting broken?

Answer:

If that was done intentionally, your fasting is broken. And if that was done unintentionally, your fasting is not broken and this fasting is correct. You gargled and some water entered into your throat unintentionally, this fasting is correct. It is similar to your sniffing water (during ablution) and it entered your throat unintentionally, this fasting is correct. But if that was done intentionally, you have committed an error and it is obligatory upon you to repeat that fasting. [Al-Fataawaa Wad-Duroos Fil-Masjid Al-Haraam of Shaikh Abdullaah Bin Muhammad Bin Humaid (rahimahullaah), page: 510] 

Abu Mu-aawiyyah (Abdullaah Al-Gambi)