An enchanted vial is made when using the binding book on an empty glass vial. The vial can be filled with water from the golden bowl (provides enough water to fill ten vials) to make holy water. They cannot be used as normal water vessels, nor for Herblore. Holy water is a usually weak ranged weapon, and is only effective on demons.
The process of making enchanted vials drains 5 Prayer and Magic levels. It is therefore recommended to make them near an altar and a bank (for stat restore potions). The Free-for-All portal in Clan Wars may also be used. Exiting the portal will recharge your prayer and stats, and the Clan Wars bank is close by.
Enchanted vials can be made in quantities of 1-10, depending on the amount of vials in an inventory and prayer/magic levels remaining. (please note: you need at least level 10 Magic to enchant.)
Enchanted vials can be made after Legends' Quest. The book of binding can be obtained in a player-owned house bookcase, and the golden bowl can be smithed with two gold bars at an anvil (note that this can fail, wasting 1-2 gold bars). The bowl(s) would then have to be blessed by Gujuo in the Kharazi Jungle, summoned by a bull roarer, also obtainable after the quest. Multiple bull roarers may be obtained by giving a cooked oomlie wrap to a jungle forester and using the drop trick.