Pathfinder 1E Creating a Holy Water Elemental

[Ezequielramone]

Well ,my group is playing whispers of the vampire's blade.
They know that the main enemy is a powerful vampire, and since one of them is playing a summoner they want to creat a "holy water elemental" in order to make real damage (the magus hit him with his blade and shocking grasp and didn't make any damage).

I need to figure out two things, how to create the elemental and the statblock.

I have some ideas, as well as them:
- Hoserule a "minor bowl of conjuring water elemental": the items says that it depends on what kind of water you use to determine the sise of the elemental (salt or fresh). I'm thinking on using a minor item because they are jus lvl 4/5. My idea is that filling the bowl with holy water will create a holy water elemental.
- Casting bless water on a water elemental: the matter of the elemental is 100% water... This will transmutate the elemental into a holy one. This has the thing that "bless water" has 1 min casting time... Maybe houseruling a mayor bless water (one lvl higher) that could transform more water in less time).
- The slam attack of the elemental could do 2d4, as the holy water does, to undead. And the rest is the same as the normal water elemental.

Those are some ideas I have. Can you help me creating the way to sommun this creature and with its stat block please?

 

[Starfox]

Rules wise this sounds like an elemental with the celestial simple template. Using bless water as a part of a ritual makes sense, or using planar binding/ally to call such a creature. The process might require extensive research and or a lot of silver dust (the material component of bless water IIR).