水 / water

水 carries two everyday readings. On its own as a noun, it's みず (mizu) — the kun reading you'll use to ask for water at a restaurant, point to a glass, or label a tap. In compounds it usually shifts to its on reading, スイ (sui), inherited from Middle Chinese — that's what you hear in 水曜日 (suiyōbi, Wednesday) and 水分 (suibun, moisture).

Beyond literal water, 水 anchors a wide family of kanji and words that touch anything liquid, fluid, or watery. As a radical it's written 氵 (the "three drops") and shows up in 海 (sea), 池 (pond), 河 (river), 油 (oil), and dozens more. Recognising 氵 in the wild is one of the fastest ways to start guessing the rough meaning of unfamiliar kanji.

水 is a pictograph — one of the oldest characters in the Chinese writing system. The earliest oracle-bone forms (c. 1200 BCE) literally drew flowing water: a vertical central current with droplets or eddies spilling off either side. Over millennia those droplets stylised into the four strokes we write today, but the symmetry around a central axis still reads as a stream in motion.

When 水 appears on the left of a compound kanji it gets squeezed into the 氵 form (three short strokes, called sanzui, "three-drops water"). When it sits below or as a base it stays close to its full form. Either way, 氵/水 is one of the most productive radicals in Japanese — a strong signal that the kanji has something to do with liquid, weather, or flow.