Control Water... how does this spell work exactly?

[Silva Stormrage]

Hello, this was a question of mine in a recent campaign as myself and the players disagreed on how this spell worked. Not really getting into the actual argument as it was minor and not super relevant it did pop into my head.

Obviously the spell allows you to raise or lower the water level. But beyond that it seems vague. Is it actually destroying/creating new water? Is it just piling the water up so it needs large bodies.

Can you use this to move water sideways? Aka moving the water out of a river and flood a bank? Or is it strictly vertical movement only? It says it can spill over the river banks in the spell description but if it just lifts water up I am not sure how it would do that.

The spell just seems very poorly worded for such a simple concept of "Control Water" and seems overly restrictive for a 4th level (Or even 6th!) spell.

What do you allow the spell to do as a DM?

[Fizban]

Between the bit about spilling over the banks and the fact that it's used as the prerequisite for the Decanter of Endless Water, I think it's pretty clear the spell is meant to be creating (or rather temporarily transmuting) more water- you raise the water level up to X, and if that means it has to make more water then it does. If you lowered the water level, when the spell ends the water comes back. Of course the Decanter is instantaneous, but the spell itself has a duration. You can "part the sea" if you've got enough depth to cut a trough, or you can make an unnatural swell that just stays there. You can make an underwater passage or flooded room temporarily navigable (though the DM might not give you air depending on situation).

I was going to say lateral movement shouldn't be possible, but yeah the riverbank thing means it must be (or "movement"), because the spell can only work within its area and it specifically keeps the raised water within that area. If you shape the spell's area so that it goes over the river and then over the bank and onto dry land, that whole area will have its water level raised- though the depth as you go up-slope will be lesser since it's measured from the water's original level. This also means that you can use a bucket or possibly even waterskin to flood a room. And with a particularly lawyery reading, by putting that bucket on a shelf you get free depth all the way to the floor, or else the water must hang in the air.

The shapeable nature of the spell clashes with the depth reading, but with that massive area (10' wide/level 10' long/level means a 10' square/level^2), if you're allowed to (S) shapeable it on top of itself you can easily flood small rooms entirely.

Really, it's spell where it's very easy to tell how it's been brought forward from previous editions and was meant to run more on DM interpretation of the well-known trope it was emulating. The 3.x wording, as is often the case, increased the level of detail and made things look more "precise," while forgetting to explain exactly what it's supposed to be capable of to people who didn't already know the existing meta.

[Silva Stormrage]

Huh I was actually curious so I looked up the 2nd edition version of the spell (Which was annoyingly named "Lower Water") and it seems you are correct where it pretty explicitly removes water "The wizard casting a lower water spell causes water or similar fluid in the area of effect to sink away."