Three-drop water radical on the left - the side-stacking form of 水. Original sense of 浓 was 'water dense with sediment, thick liquid'; from there the meaning broadened to any concentrated quality. Family includes 淡 (dilute, opposite), 稠 (viscous).
Right 农 supplies the sound nóng exactly. Simplified from traditional 農, with the phonetic retained in stylised form. Same phonetic family in simplified script: 脓 (pus), 哝 (mutter). All share both the sound and a faint sense of 'thick, dense.'
