Ghosted this topic but still hate the way things are because they didn't magically change like I hoped they would (the genie lamp I found was a scam).
Since initially creating the topic I've discovered the existence of several other water related tags. Gonna list them with their main wiki and tag count (at time of writing) for my benefit and for the benefit of discussion. Feel free to mention any I missed.
Completely under water
underwater 24381 "An image that is shot from underwater, or that takes place completely underwater."
submerged 4171 "A character who is completely underwater."
immersed 135 "Used when an object like a building or a vehicle is completely in some liquid, such as water."
Waist Up
partially submerged 37568 "Standing in water more than waist deep, or lying, sitting, or kneeling in shallow water."
partially immersed 265 "Used when an object like a building or a vehicle is partially in some liquid, such as water."
Waist Down
wading 40528 "Standing or walking in water less than waist deep."
soaking feet 9721 "Sitting or resting with one or both feet in the water (or another liquid)."
On the surface of
standing on liquid 2976 "When a character is standing on the surface of a liquid, most often water."
kneeling on liquid 145 "When a character is kneeling on a liquid, most often water."
sitting on liquid 101
walking on liquid 999 "When a character is walking on the surface of a liquid, most often water."
running on liquid 137
on liquid 128
Things that currently class as partially submerged to some degree
lying on water 936 "A character is lying on a body of water."
sitting on water 742 "To be gardened/deleted. See applicable tags listed under in water (placeholder tag). Most likely partially submerged. Under discussion in forum #232427, possible use for standing on liquid like scenario but for sitting or lying without visible submersion or glass floor."
on water 701 "A person is atop a body of water, usually by being partially submerged in a low pool, or floating inside an innertube."
afloat 4968 "Floating in water or other liquids."
Misc
afloat 4968 (see above)
shallow water 2461 "Water that isn't particularly deep, the bottom is usually visible."
partially underwater shot 2291 "When the image is divided into two by the water's surface; in other words, the "camera" is partially submerged."