noun
gray-water system; recycled wastewater system
Technical term for a system that treats and reuses wastewater from sinks, baths, etc. for non-potable purposes like toilet flushing or irrigation.
このビルでは中水道を導入して、トイレの洗浄水に再利用している。
This building has introduced a gray-water system and reuses the water for flushing toilets.
Compound of 中 (middle, intermediate) and 水道 (water supply), referring to an intermediate water system between clean water supply and sewage.