A water purifier is an electro-mechanical device used for purifying water of contaminants. In a self-contained environment, like the Vault-Tec Vaults, the water purifier is a component of the water systems.
Vaults
In the sanctuary of the Vaults, the water purifier is located in a secured room. This room in Vault 101 is the filter room in the reactor sub-level. The water purifier's cleanliness and maintenance fall under the purview of the maintenance department. On July 12, 2268, the technician Stanley Armstrong with the aid of Andy repairs the water purifier.
Other water purifiers
Some of the cities in the Wastes have custom-made purifiers, such as Megaton. One of the largest water engineering projects in the 23rd century is Project Purity, where, under the leadership of James, scientists attempted converting the Jefferson Memorial into a giant water purifier for the Capital Wasteland.