水库
shuǐkù · HSK 5
reservoir
💧 水 (water) + 库 (storehouse) = water storehouse
水 means water and 库 means warehouse or storehouse (the same 库 as in 仓库 warehouse and 车库 garage). A 水库 is literally a water-storehouse — the Chinese term for reservoir.
水 — pictograph of flowing water
水 is a pictograph depicting a stream of flowing water, with the central line representing the main current and the side strokes showing splashing droplets or ripples. In oracle bone script it was drawn even more clearly as a wavy vertical line with branches. It retains its original meaning of 'water' and also serves as a radical, often appearing in the compressed form 氵.
库 — 广 (shelter) + 车 (cart/vehicle)
库 is a semantic compound combining 广 (a roof or shelter) with 车 (cart or chariot). Originally it depicted a building where chariots and weapons were stored, hence an arsenal or storehouse. The meaning broadened over time to any warehouse, treasury, or storage facility.