Items, Z-Crystals, #819
Waterium Z appears in 4 version groups since Generation VII, a Z-Crystals item in the Key Items pocket
PokéAPI item 819 of 2,223, Z-Crystals category, Key Items pocket
Effect, in PokéAPI's words
Waterium Z: “Held: Allows a Pokémon to use the Z-move equivalents of its Water moves.”
Games
Waterium Z is listed in the text of 4 version groups, first in Generation VII
Game index by generation
IIIIIIIVVVIVIIVIIIIX
Named in
Sun and MoonUltra Sun and Ultra MoonLet's Go Pikachu and Let's Go EeveeSword and Shield