clean-water reservoir
A reservoir that stores clean or purified water, as opposed to raw water. Often used in water supply contexts.
この浄水地は市の飲料水を貯えている。
This clean-water reservoir stores the city's drinking water.
Compound of 浄水 (clean water) + 地 (ground, place). The exact historical derivation is uncertain, but the term is used in modern water supply engineering.