Removing salt from seawater doesn't make it drinkable fresh water-- it's also got a lot of sulfates in it (never swim in the ocean if you colour your hair!) and it's alkaline due to high amounts of bicarbonate resulting from dissolved CO2.
That said, it probably fits the medieval paradigm, but the biologist in me is gonna grind my teeth and grumble whenever I see it anyway.
Sulfur and and soda are minerals, no?
And colour? Really? Do I need to imagine you with an English accent now?
Ok, so there is a Base 15 Guideline for Destroy the Saltiness of Water, which when you work it all out, it's exactly the same level/build point cost.
"Mineral" is not synonymous with "salt."
I buy most of my books from amazon.co.uk, so maybe that's why I tend to use British spelling conventions (-our instead of -or, doubled consonants, and I use the Oxford comma). Incidentally I did learn English as my second language by watching the Beeb, but while I say "aluminium" and "rubbish," and I had a really weird Korean/British/Ebonics thing going on as a kid, now I speak perfect Northern California / media American English. Though when I get really angry I speak East Oakland, and when I get really drunk I speak West Texas.
The idiosyncrasies of being from Everywhere 
(The joys of having your internet connection die while you're working on a big ol' post like this. And so, three hours later...)
Not sure I'm seeing this the same way the book does. I'm following PeCo base 4, with +1 Touch, and I'm following the +10 to the Lab Total for Unlimited Uses. But I don't think the Aquam requisite requires an added magnitude: it "simply allows the spell to have its effect" and "do(es) not add to the spell level, as the difficulty of doing such a thing is already accounted for in the guidelines." Akin to the Animal requisite for Eyes of the Cat. So, I'm inclined to call it a Lab Total 15. That's assuming that you want a magic chamber pot that you have to manually activate every time you want it emptied. If you give it an Environmental Trigger ("Every time it's sullied, so to speak," that would add +3, which would wind up being about the same vis cost and 1 BP less.
Yeah, it feels off to me too. But it got published this way, nothing in the errata, and nothing on the forums. But it's got a new Baseline, it uses...wait just a moment. Whoa, nelly, did they blow it.
Perdo Aquam guideline from the core rulebook – Level 15, "Destroy one property of a liquid (like alcohol's ability to intoxicate or sea water's saltiness." (emphasis mine). But it says nothing about Terram requisites.
So, that would be Base 15, +1 Touch, for an Effect level of 20. But you don't need concentration (once something's destroyed, it stays destroyed, generally), and are you going to be filling it up on average once an hour? If it's a good-size cask, say, the size of a wine barrel (about 60 gallons/225 liters), you shouldn't need to refill it more than once every couple of days. So, one use a day for no change to the LT. Still looking at cheaper than what it has by the book.
That's okay...my excuse is that I learned to write, and spell, in England. So I have to make a conscious effort not to write things like grey, colour, favourite, etc. Which is usually not worth the effort.
And West Texas? Hill country I can see...but West Texas?
The device effect level drops to 15 now, and it comes out to 2 build points less according to MC.
The Cask of the Naiad 21
Vis Capacity: 10; Effect Name: Cleanse Gaia's Tears; Effect
Level: 21; Effect Details: R: Touch, D: Mom, T: Ind,
Frequency: 2/day; Destroys the saltiness of salt water; Arts:
PeAq 20; Design: Base 15, +1 Touch
I dropped the item effect down to 21, adjusted the base to the correct guideline (Useable twice per day, a just in case thing) BP cost of 8.
Personally I would give it a 4-5 uses per day. There are a lot of covenant members, animals and such.
That's okay, it's part of Talia's 75 personal build points, so presumably designed to accommodate the size of her crew. If she has the lab notes, we can probably make more if we want.
Whether or not she has the lab text for these items is mostly up to your generosity. I could easily see that she has acquired the items from shipwrecks, salvage, booty or rewards. These are items she likely did not make herself.
Let's go with the booty-plunder thing. If we want, maybe we can have it Analyzed and figure out how to make more.
There are some new spells in the Library.
The Bound of Homecoming is a ReAn version of The Leap of Homecoming.
Cabin of Earthen Wood is a CrHe(Te) Ritual that creates a structure (much as Conjuring the Mystic Tower does) made out of wood as hard as stone. Base is 3 ("Create wood in an unnatural shape, such as a living wall or bridge"), R: Touch (+1), D: Momentary, T: Individual, +2 to "create treated and processed Herbam products," +3 for size, +1 for the Requisite.
Clouds of Snow and Sleet is a variation of Clouds of Rain and Thunder.
Craft the Lasting Pier is a CrHe ritual which is used to create the pier that encloses the two islands. Base is 3 ("Create wood in an unnatural shape, such as a living wall or bridge."), R: Touch (+1), D: Momentary, T: Individual, +2 modifier to "create treated and processed Herbam products," +5 for size (the pier is about 1,750 in total length and 8 feet wide, while the piles along the outer leg must reach almost 250 feet).
Create a Statue For the Garden is a MuCo(Te) spell that allows the caster to transform the target into an unmoving, unbreathing stone statue that is practically immune to the elements for the duration of the spell. Base is 25 ("Turn a body into a solid inanimate object"), R: Touch (+1), D: Sun (+2), T: Individual, no modifier for the Requisite (included in the guideline difficulty), +1 for increased size.
Gift of the New Body is a variant of Disguise of the New Visage which allows the caster to utterly change the body shape/size/gender/features of the target (e.g. turning a tall, skinny man into a Rubenesque woman). R: Touch (+1), D: Sun (+2), T: Individual. This is actually a shade easier than Disguise of the New Visage, due to the Target being Individual rather than Part.
The Seat of Nature turns any plant, bush, or tree of up to ten cubic paces (roughly 270 cubic feet/7-2/3 cubic meters) into a chair, bench, couch or other similar type of furniture. R: Touch (+1), D: Sun (+2), T: Individual, +1 Size , +1 to turn into treated/finished material.
Seven-League Bound is the ReAn equivalent of Seven-League Stride.
Level 20
Shipwright's Delight: River Barge
Base 2, create a finished plank of wood, R: T, D: M, T:Group, Ritual Size +3
This spells creates up 10,000 pieces of wood, each up to 1 cubic pace in total size. The individual pieces vary in shape according to the design of the spell, as per Conjuration of the Seaworthy Cog, this spell must be invented for different types of ships.
This spell probably needs some kind of Int+Finesse roll to go along with it considering the number of pieces. I think I did the math and the volume of wood created (base form is 1 cubic pace) would be more than enough for 3 vessels, I just want enough for 1 vessel. Would having the pieces shaped correctly aid in construction or is that too much to ask?
If Talia uses Eilon Chon, and does this in Spring 1223 her LT is
Cr 13+3 + He 10 + Int 3 + MT 1+2+ specialty 1 +aura 6+ focus 10 +lab 7 =56, which suggests I could make even more wood or ad +1 for Complexity or something...
The math on the spell description looks good. I'm thinking a Finesse roll vs. an Ease Factor of (12 – appropriate Ability, such as Shipwright) to get the planks all shaped correctly. Failure means that the planks are there, but some might need a touch-up to get them to fit right, like some planing on one of the edges or something. A botch means you have about the right number of planks but it's going to take major work to make it right (e.g. every plank needs to be planed or re-cut).
Sound reasonable?
Yeah, it means she's got a better than 50% shot at pulling it off.