How many hours does it take to rehydrate after dehydration?

Degree dehydration: It really depends on how dehydrated you were in the first place before starting rehydration. If dehydration is moderate to severe, you will likely receive a 1-2 liter bolus of IV fluids, with the IV line wide open, allowing the fluid to get into you as quickly as possible. It can take anywhere from 30-60 minutes to get 1 liter of fluid into you in this manner.