There are nine acts which invalidate fast:
Eating and drinking
Sexual intercourse
Masturbation (Istimna) which means self abuse, resulting in ejaculation
Ascribing false things to Almighty Allah, or his Prophet or to the successors of the Holy Prophet
Swallowing thick dust
Immersing one's complete head in water
Remaining in Janabat or Haidh or Nifas till the Adhan for Fajr prayers
Enema with liquids
Vomiting