沟
goū · HSK 5
ditch
🕳️ sounds like 'go' — water goes down the ditch
沟 pairs 氵 (water radical) with 勾 (gōu, hook/curve) as the phonetic. Water + hook-shape = a curved channel cut for water: a ditch, gutter, or groove.
沟 — water radical 氵 + 冓 (gòu, phonetic)
A semantic-phonetic compound: 氵 (water) gives the meaning, while 冓 supplies the sound. Originally referred to a water channel or ditch dug for irrigation or drainage. The meaning later broadened to any groove, trench, or furrow, and figuratively to communication channels (as in 沟通).