The mechanism that defines bioavailability centers on how our bodies absorb the substances we ingest, inhale, or receive intravenously. In this case, bioavailability focuses on how much of a substance enters the circulatory system. For example, when you receive a drug intravenously, the bioavailability is 100% because it is introduced directly into the bloodstream.
When you ingest products, the amount of CBD that enters your bloodstream depends on how well it is absorbed. While water is readily absorbed, fats and oils must first be broken down by bile and then metabolized by the liver.