Those sound incredibly useful for investigating miracles, and if Select Artigas turns out to be interested in helping with that they could probably get the Vatican to sign off on his papers and salary legitimately, assuming they can determine for certain that his powers aren't from a demon. It really doesn't sound like they're from a demon; powers granted by demons are rarely so benign.

"Which orisons are you holding today? Is it alright if we perform some experiments to verify their capabilities? ...Also, just as a precaution, have any of your supernatural abilities been known to backfire such that they technically achieved the advertised effect while entirely subverting your intent?"

Oh no he has to admit he spent a completely inappropriate amount of time wondering if they would poison him. "Today I have Create Water, Guidance, Light, and Detect Poison. I... don't think any spells I know of have that problem, but it's possible that... a hostile spellcaster could co-opt a summoned creature, maybe? And if I were enchanted out of my right mind I might cast allied spells on enemies or vice-versa? I think the thing you describe is a known hazard of the spell Wish but it is a ninth circle arcane spell, I can't cast it and will never be able to."

"What does Guidance do? ...For that matter, what does Light do?" Presumably it's light-related but there are a number of plausible light-related effects it could have.

"Light makes an object glow; Guidance makes me slightly better at one thing I do in the minute following its casting and I often cast it dozens of times a day."

"Of the four of those, Create Water sounds easiest to test. What sort of receptacle will you need to demonstrate it?"

"...I can make up to ten gallons but it can be less and I'm fairly good at shaping it how I like, so if you want vapor I don't even need a container but any cup or bowl will do if you prefer."

"If you can do it multiple times, it would be useful to see a demonstration of both vapor and liquid water, but liquid water will work better for the tests I have in mind."

He explains what he's doing to Roberto, leaves the room, and returns with a metal bowl and some unfamiliar-looking scientific equipment.

"When you're ready?"

"Now is fine."

"Create Water."

That certainly does appear to be miraculously-appearing water.

What happens if he uses this equipment here to run some tests on it? Is it chemically normal for water? Does it have the impurities you might expect from, say, tap water, or is it pure water? Does it have a basically normal (tiny) fraction of heavy water for a naturally-occurring water supply, or exclusively the regular kind with normal hydrogen atoms? If he removes a small amount and boils it, does it boil at a normal temperature given local conditions?