Water Cup

The Water Cup is the small healing item of The Archives, and it does nothing until it is filled. At a water dispenser the cup can take hot water, cold water or poisonous purple water. The wiki's tip is to add hot water and then mix it with cold water to get the correct cup, which heals about 5 HP. Drinking purple water instead deals around 10 HP of damage, and so do cups of only hot or only cold water. It takes ten of those damaging cups to kill a player.

A cup that costs no space

Only one cup can be held at a time, and the player can have the item in the inventory only once until the water is drunk. In return, it takes no inventory space, so holding an empty cup has no downside. The wiki also calls it the only minor item that can be stored in the Rift, which makes it a convenient way to occupy an empty Rift and swap items later.

Where the water is

Every last room of each sector is guaranteed to have a water dispenser, and so is the floor with Honcho. One bug empties the cup when the player exits The Archives onto another floor.