溝
どぶ · dobu · JLPT N1 · noun
ditch
🕳️ Water radical 氵 + 冓 (kō, the sound part) = a ditch that carries water
The left side 氵 is the water radical, so the character marks something watery. The right side 冓 supplies the sound (こう). A dobu is a drain or gap where water runs.
みぞ · mizo · JLPT N1 · noun
ditch
🕳️ Sounds like 水 mizu (water): a mizo is the channel where the water runs off
The left part 氵is the water radical, and 冓 suggests things built or fitted together. A ditch is a water-carrying channel built into the ground, so the water radical gives the meaning.