Radical
氵 (water) +
圭 (jade tablet, just phonetic) — water collects in a low place, hence 'hollow / depression.' Most common compounds:
水洼 (shuǐwā, puddle),
低洼 (dīwā, low-lying),
洼地 (wādì, depression / wetland). The traditional form
窪 uses
穴 (cave) instead, reinforcing the 'hollow' image.
