红药水

• 糹(thread; silk fiber)RADICAL
• 工(craftsman; work)PHONO-SEMANTIC

A thread dyed by the craftsman becomes bright red.

• 艹(grass; plant)RADICAL
• 约(promise; bind)PHONETIC

Medicine is made from grass and plants, sounding like "wish" or "promise".

• 水(water (pictographic))ASSOCIATIVE

Water mimics the flow of running water with ripples on both sides.