A small glass bottle filled with water.
The bottle acts as a Familiar and follows closely behind Isaac. It breaks when he receives damage, causing a blue puddle of Creep to form that will damage enemies that come in contact with it. The puddle disappears after a short period of time.
No new Creep will appear until the bottle is reformed, which is caused by entering another room.
- Holy water is water that has been blessed by a saint or clergyman. It is used to confer blessings upon believers, as well as baptism.
- The design of the item is based on the Holy Water sub-weapon from the Castlevania series of games.
- A shooting Familiar taken will transform into Brother Bobby or switch places with him upon picking up Holy Water as with active use of Best Friend. It will revert back to normal once the glass bottle breaks, but will turn into Brother Bobby again upon entering another room. Little Chubby prevents this glitch while it is not actively attacking. The priority for replacement is (highest to lowest): Isaac's Head, ???'s Soul, Little Steve, Demon Baby, Little Gish, Rainbow Baby, Harlequin Baby, Ghost Baby, Sister Maggy, Robo-Baby and Abel.