water radical variant (no. 85)
氺 is a variant shape of the water radical, used as a component in other characters. It does not carry an independent meaning beyond representing water in this specific visual form.
氺 is a graphical variant of 水 (water), used as a component in certain characters. It developed as a compressed or stylized form of the water radical for use in specific positions within a character.
Picture 氺 as a small, squeezed version of 水, like water being poured into a narrow container. It still represents water, just in a different shape.
For スイ, imagine a swimmer gliding through water: swim -> スイ, and the water radical 氺 represents that water.