water
水 centers on water as a substance: the liquid itself, bodies of water, and anything fluid or aqueous.
water (esp. cool or cold)
bathing suit; swimsuit; swimmers
water supply; water service; waterworks; tap water
hydrogen (H)
water; liquid; fluid; moisture; humidity; sap; juice
level; standard
Wednesday
diving; submerging; going underwater
swimming
horizontal; level; even
perfume; scent
drainage; draining; pumping out (water); sewerage
underwater
aquarium (building)
Wednesday
flood; flooding
water tank; cistern
light blue; pale blue; aqua
water's surface
on the water; aquatic
aquatic products; fisheries
seawater; saltwater
waterproofing; making watertight
(rock) crystal; high purity quartz
水 is a pictograph of flowing water, with the central stroke representing the main current and the side strokes suggesting ripples or splashes.
The central vertical stroke is a stream of water, and the four side strokes are splashes or ripples. Together they form the character for water.
For スイ, imagine a swan gliding on the water: swan -> スイ, and the swan's smooth movement matches the flowing shape of 水.