Source Starfinder Armory pg. 28
A holy water weapon is infused with the blessings of one or more good-aligned deities (most commonly Hylax, Iomedae, or Sarenrae within the Pact Worlds, though devoted followers of any good-aligned deity could create such weapons). It damages only undead (regardless of alignment) and outsiders with the evil subtype, and even those creatures suffer no effect (and show no sign of their nature if it is not already obvious) with a successful saving throw. Crafting a holy water grenade requires the blessing of formally trained priests of a good deity, though a character of any alignment can do the actual crafting.
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