Left water radical - three water drops, the indexing component. 氵 marks 湿 as a water-state word: damp, moist, humid. Same radical anchors a huge water family: 河 (river), 海 (sea), 油 (oil), 汗 (sweat) - anywhere liquid is involved.
Right 显 supplies the sound (xiǎn → shī, drifted considerably - historically the right side was a different graph 㬎 that the simplification reform replaced with 显). Modern reading is opaque; treat as a learn-by-rote phonetic anchor.
