You regain one expended spell slot when you drink this potion.  The level of the regained slot depends on the potion's rarity, as shown in the Potions of Arcane Recovery table.  If a spell slot your regain is higher the maximum spell slot level the potion would allow you to recover, the new slot is the highest level that potion can restore.  Whatever its potency, the potion’s transparent liquid smells and tastes like vinegar.

Potions of Arcane Recovery

Potion of Arcane Recovery (Common).  When you drink this potion, you regain one expended spell slot. If the expended slot was of 4th level or higher, the new slot is 3rd level.  The transparent liquid smells and tastes like vinegar.

Potion of Greater Arcane Recovery (Uncommon).  When you drink this potion, you regain one expended spell slot. If the expended slot was of 6th level or higher, the new slot is 5th level.  The transparent liquid smells and tastes like vinegar.

Potion of Superior Arcane Recovery (Rare).  When you drink this potion, you regain one expended spell slot. If the expended slot was of 8th level or higher, the new slot is 7th level.  The transparent liquid smells and tastes like vinegar.

Potion of Supreme Arcane Recovery (Very Rare).  When you drink this potion, you regain one expended spell slot of any level.  The transparent liquid smells and tastes like vinegar.