water level; hydrostatic level
A tool that uses water to determine a horizontal plane, similar to a spirit level but employing water instead of a bubble.
昔の大工は水秤を使って水平を取った。
Carpenters of old used a water level to establish a horizontal line.
Compound of 水 (water) and 秤 (scale/balance), referring to a device that uses water to measure levelness.