This one isn't really inspired by the Harry Potter books is it? 
Not directly, no 
It is not truly Evil with capital "E" until it also blocks the use of teleportation spells or devices
A ward stops teleport spells as well, no? Or are we in muddy waters again? (likely)
Disgusting, but ineffective as a means of execution unless the cell is really, really, tiny (in which case the character will probably die of other reasons first). A sphere 3 meters (10 feet) in diameter, which is a fairly small cell, takes over half a dozen years to get halffilled by the average urine and feces of an adult. Of course, long before that time, urine (which is about 2/3 of the volume) has evaporated and escaped the ReCoAq ward; and so it takes about two decades to fill half the cell with solid matter -- which by that time probably has probably spontaneously devolved (by Ars Magica physics) into worms, Terram, or other similar stuff not blocked by the ward.
urines cannot scape when in vapor form. Vapor is still affected by aquam.
Xavi
I would contend it's Auram -- like mist and clouds.
Serf's Parma, but IIRC it used to be that in 4th edition, but they changed that in 5th edition since vapor is a natural state of aquam, so you can affect vapor, liquid or ice with Aquam. The current state does not change the fact that it is still aquam.
In any case if you want to fill the place with crap, you can always make it small (1 metre in diameter). it speeds things up notably, and makes the prisoner markedly more unfomfortable than in a 3x3 cell. I doubt that someone that wants to bury someone in his own shit cares much about the comfort level of his prisoner after all. :mrgreen:
Xavi
As far as I can tell Aquam only affects liquids. You can use Rego Aquam without requisited to change a liquid into its corresponding vapor or solid (e.g. water into ice) but once it's no longer liquid it's no longer Aquam.
The point is that if you imprison someone in such a small place, he'll still die of infected bedsores before drowning takes place.
Ladies and Gentlemen,
You have disgusted the Internet. Congratulations! 
Let's go back to the math...
I made no such claim!
It is merely 'really mean'!
Evil is something very different 
Salvete, Sodales!
Well, the guidelines for PeCo and PeAn are mostly interchangeable, at least those for causing wounds and pain are. And among the PeAn spells there is an example of this grade 4 guideline ('Agony of the Beast'). For consistency's sake I'd stay with this and would allow additional magnitudes for stronger pain (probably +3 to the stamina check's difficulty level per magnitude). If the effect goes on for a while it might help with interrogation and such (give a bonus to the inquiasitive turturer's role), and really long term exposure might lead to unpleasant personality flaws.
Vale,
Alexios ex Miscellanea
I knocked up two versions, the first as a base effect using the default guideline (base 4) and another using the immobilise guideline (base 5) with Voice and Group effect added. The guide for a Stam check in the post is good, but I'm not sure that size has a bearing.
Invoke the Agony of Man
Perdo Corpus 15, R: Voice, D: Conc, T: Individual
Inflicts the target of the spell with wracking pain, almost completely disabling them. To make an action the target must succeed a Stam + Size stress of 9+.
(Base 4 to cause a person pain, +2 voice, +1 concentration)
And..
Invoke the Horrific Cacophony
Perdo Corpus 35, R: Voice, D: Diameter, T: Group
This spell inflicts the targeted group of up to 100 standard sized people with physical pain so severe that they can do nothing else except writhe in agony, and perhaps very slowly crawl away.
(Base 4 to cause a person pain, +1 to boost the effect to the same level as ReCo immobilizes the target, +2 Voice, +1 Diameter, +2 Group, +1 to affect up to 100 targets at once)
Second is set to Diameter so that the bad guy can monologue for up to two minutes before dealing with the PCs.
cheers IBT
There perhaps is the opportunity to ReCo a superfast digestion track which would make the victim endlessly hungry and thirsty, thus you could feed and water them about twenty or thirty times a day... it would stack up pretty fast.
Okay, to rerail the thread and polish the spell before posting it in the Grimoire thread, it looks like we have:
Cruciatus Curse (Perdo Corpus 20)
R: Voice, D: Concentration, T: Individual
This spell causes the target excruciating pain, and he must make a Stamina + Size roll against an Ease Factor of 9 to be able to do anything but writhe in agony. Enduring Constitution adds 3 to the Stamina roll; other Virtues, Flaws, or Abilities that affect the ability to endure pain may also modify the roll as appropriate.
(Base 5, +2 Voice, +1 Concentration)
Seconded.
Although I would suggest you add 'Perdo Corpus level 20' in there somewhere, before you add it to the Grimorie
Salvete, Sodales !
PeCo 15 is correct for this version (cf ironboundtome's version 4 posts above) as the base is 4 not 5. In order to mimick the Harry Potter spell, I'd add 2 magnitudes and raise the ease factor to 15. Fighting through the pain should somehow be possible but is supposed to be really hard.
Vale,
Alexios ex Miscellanea
Following the rules for resisting poisons from the Cr Aq guidelines for poison raising the Ease factor to resist means raising the magnitude of the spell by one per +3.
Base 4 might be enough, but the Ease Factor should not be too high here. Basic poisons spells start with Ease factor 3! And IMHO they are not interesting before they're raised to at least 9, otherwise it is simply too easy to resist.
People argued for using Base 5 for crippling pain such as this. Perhaps the base for is for something modest like EF 6, which means raising it to a whopping 15 means +3 magnitudes.
This makes sense to me.
It shouldn't be too easy. After all why isn't this THE spell used by Hoplites to catch criminals alive?
When things aren't defined in iron clad terms in RAW I tend to err on the side of caution, in fact so does my entire gaming group. Because things aren't fun if they are abusive.
I'm not saying anything against the Cruciatis spell - in fact i like it a lot - but just consider how other guidelines make rules about "natural resistance rolls".
The trick is to decide what the Basics are. IMHO the resistance rolls for CrAq poisons seems too easy, so you need very high spells to be efficient. But that's ok, after all it isn't the most commonly known way to harm people. Ignem is!
So if a Base 4 PeCo inflicts crippling pain with a Stm+Size vs. EF 6 to resist that's a good start, with +1 mag giving +3 EF. And people can boost it as much as they want. Or it may start out with other numbers.