Are you trying to do this in combat, or just looking for creative ways to drown characters?

Resilient sphere is lower level than force cage (and smaller, so it's quicker/easier to fill), if that helps.

Also, for a trapped opponent holding his breath under water, summon water elementals to attack him; by RAW, a fighting character drowns MUCH faster than one just holding his breath.

For simply malignant purposes under controlled circumstances (read: "torture & execution"):
(1)unstopper a decanter of endless water in "stream" mode.
(2)apply sovereign glue to rim.
(3)press to victims lips to seal.
(4)watch water come flooding out nose until victim stops thrashing about.

Or just tie down enemy, and summon water elementals to sit on his face.

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