Ummmmm.  Boring?

Wait until one of your players tastes it. It isn't that boring, anymore. 

If a full 15ft cube's worth of water was used to make the pebble, it will have 25,245 US gallons of water to smash in some poor NPC's face. For anyone who wanted to know.

Quote from DarkThor1987 >>

If a full 15ft cube's worth of water was used to make the pebble, it will have 25,245 US gallons of water to smash in some poor NPC's face. For anyone who wanted to know.

 Which, incidentally, makes this dust tremendously good against fire elementals as well, due to their "water suspectibility" feature:

Water Susceptibility. For every 5 feet the elemental moves in water, or for every gallon of water splashed on it, it takes 1 cold damage.

25 thousand gallons, you've said? Even assuming that not every single gallon is gonna touch the elemental, the damage would still be instant kill on a poor bastard.

Not to mention the sheer force of that much water instantly spawning from a point in space. This is definitely a creative player's item, assuming their DM isn't an uptight RAW worshipper... and that the player doesn't abuse the shit out of this "boring" item.

And as a trivia for non-Americans: 25,245 US Gallons equals to 95,562 liters. So, yeah... Nearly 100.000 liters of water you hold in a bead, and can instantly spawn anywhere.

Seeing as it’s just uncommon, I don’t see why a party can’t find/buy/make maybe 10 pouches for a maximum of 2,524,500 gallons of water (9,556,200 liters).  If your DM has a BBEG with:

-A need to breathe

-Water susceptibility

-The ability to decay

-Really anything against water

You can easily trap them and drop a good amount of water on them.  Besides, take all 100 pellets, put them in a bag, and toss it in a Tarrasque’s mouth.  Either it spends a few turns coughing out all the water, or the party evades it for 10 minutes or so for it to drown.

Then, as I read fine this description, the pellet have an undefined weight ???

What could happens if I tight some of those pellets to form a safe surface ( just to make a provisional boat, or a surface to jump over ) ??

Quote from DaBamboy >>

 

You can easily trap them and drop a good amount of water on them.  Besides, take all 100 pellets, put them in a bag, and toss it in a Tarrasque’s mouth.  Either it spends a few turns coughing out all the water, or the party evades it for 10 minutes or so for it to drown.

 First, you have to get a successful attack dice throw at least. Then, if the Tarrasque don't evades the chance of being drowned by this "watery overdose", you'll get the chance of escaping from this monstruosity who chases you and your party.

But, I think I have a better strategy:

First get a dozen of those pellets. Later, using the spell Mold Earth just to create an improvised lake on a nearer hill or mountain, blow the water on it.

And, do you know how funny is watching the lake blowing the water ( as an avalanche ) over the Tarrasque ??? 

To do this last part, you only have to "open a hole" on the lake.... and TADAAAAAA !!!

it would be paired great with 'create water'..then as long as you have more dust you could be a water ninja and not have to waist to many of your spell slots

15 cubic ft is 112.208 US gallons, which is still a lot but not anywhere near 25k

It's not 15 cubic ft; It's a cube 15ft across. That's 3,375 cubic ft.

My bad thanks!

Would firing one pellet from a sling at a hard surface fulfill the "use an action to smash the pellet against a hard surface"? Can it be Thrown, to "smash" it? 

(Presumably, Moving across it on a hard floor won't "smash" it, because Moving does not use an Action... but:)

Do we have any flexibility in how we smash the pellet?  IE: Can we use a tool? Can we throw it?

You'll always have whatever flexibility is allowed by your DM! For the sake of simplicity, I'd dictate that it's pretty much a hollow glass marble. When shaken, the fluid inside doesn't behave like a couple drops of water but instead looks like an entire micro ocean full of waves and swells. The glass would be thick enough to bounce from a simple drop 5 or 6 feet, but thin enough that, if thrown or slung with any intention, it should break against a hard surface.

I like that. Nice description, too. 

I wonder what the intent was, though. Many items are obviously written with intent to limit their use to the described method alone (Magic Pebble, for instance, would be enormously better if you could throw all pebbles at once), so I'm not confident that the wording is intended to allow Slings, or breaking a pellet unintentionally, etc. 

Vague wording or unclear meaning can really bog down the action at a table, with semantic discussions unforeseen during session zero. Leaving an esoteric ruling to each DM's judgement call, is akin to saying "go ask your mother", & makes the game harder to play. 

House rules aside, I'd love to hear an official statement on the intent, with this item's usage.

Bless the water to make a holy hand grenade

You can produce 12,5 tonnes of water wgerecer you want just by tape the perl to the end of an arrow. This is excellent crowd control, probably can erase a house out of the way. I think, it's not boring.

Well 15ft on a side means that's a cube 15ft long, 15ft wide and 15ft tall. That's 100k liters of water...or 100 TONS of water to throw at something (or someone). If that doesn't cause serious damage, I don't know what does!

"An elemental composed mostly of water that is exposed to a pinch of the dust must make a DC 13 Constitution saving throw, taking 10d6 necrotic damage on a failed save, or half as much damage on a successful one."

How much is "mostly"? I mean, a human is 70% water...

Effect on ice? The same? Throwing this on Auril 2nd form???

1 Ceremony spell creates 1 vial of Holy water / 25gp - hardly efficient for this usage. Unless we include homeopathy and claim that the more diluted the holy is in the water the more effective it gets.