^I don't know if you were being sarcastic or serious.
If you're going to make this a skill, here's what I recommend.
Making Holy Water enabled.
rF 30% success rate using water sunlight+mana herb.
Making Holy Water enabled, Making More Holy Water per attempt enabled, Rank of enchant skill will increase Success Percentage.
Making Holy Water, Massive Holy water, multiple production per attempt enabled.
Total AP estimate 124
INT total, 55
Will total, 30
Dex + 12
Ingredients needed per attempt regardless of rank: 3 Mana herb 3 Sunlight herb 1 Water.
Rank 1 success rate 90% for regular HW
15% for massive
20% for multiple production(Min-max 2-5
Obviously, for user created holy water, Skill training would be hell.
So GL and now it's time for you to obsess and assess about the realism of lack thereof of this skills details XD