boil (something) away
To boil a liquid for so long that it evaporates. If you don't put the pasta in the pot soon, you will boil all of the water away.
boil something away
1. Lit. to boil a liquid until it is gone altogether. She left the kettle on and boiled the water away. Boil away some of that water.
2. Lit. to remove a volatile chemical from a solution by boiling. Boil the alcohol away or the sauce will be ruined. You should boil away some of the liquid.