The Create Water spells reads:
In an open container, you can create up to 10 gallons of drinkable
water. You may also produce a rain that falls within a 30-foot cube
and extinguishes open-air flames.
Must the container be filled by the water created? IE, a horse trough or sinkhole would not be valid targets, since they can hold more than 10 gallons of water?
If not; what prevents me from simply choosing the room I'm in as the container? For example, creating 10 gallons worth of water on the floor with the intent of freezing it to make ice terrain?
Or further, choosing the room and creating a gush of water over an unruly bar patron to "cool them off" – I can create rain, does something restrict me to Creating Water on or very close to a surface?
Best Answer
I believe the answer to your question may lie within the spell's written affect, You can create up to 10 gallons of drinkable water.
There is nothing that specifically states it must fill the container, but something that does state you can create up to 10 gallons of water (as in you can create between 0 and 10 gallons of water). So long as it can be an area with an open space, you should be able to create water inside of it.
Note: the GM has final say, given they have more power than the gods in their universe.